Dunno much about AA, so I can't help you there. You can open multiple United MP accounts (but you can't merge them). Just ignore the one you just created and go ahead with the referral. I'll give it to roadtripmap, since he offered first

RE *A and elite status: Yes and no. It depends on who the partner is and what fare code. Some airlines, like ANA, give full RDM (redeemable miles) but only 25% or 50% EQM (elite qualifying miles), and then only on certain fare classes. Air Canada, on the other hand, I believe gives full 100% RDM and EQM, but their miles don't count toward earning free upgrade certs. The list goes on and on. Generally, I'd say for a UK-based flyer, United would be your best *A choice since you can get almost anywhere on their metal (and therefore earn the most status/RDM/free upgrades) for often the cheapest ticket. Plus United has the best community here on FT

Flights on AA, its oneWorld partners (note: not all its partners) and Alaska Airlines count toward status, including the Challenges.

One exception that may affect you is BA flights to/from the U.S., which earn no AA miles for reasons discussed at great length in other threads. This can be avoided by either flying AA across the pond or flying BA to Canada or another North American destination.

Also, some deep-discount partner economy fares earn fractional, occasionally zero, AA credit. (BA's fares earn 25 percent credit. The full list, by airline and specific fare classes, is on aa.com.) This can sometimes be avoided by booking the same flight under an AA code-share number, in which case AA mileage-earning rules apply, but that may involve a higher fare and can sometimes be done only in conjunction with an AA flight from the U.S. to wherever that flight departs.

No, the Challenges now work differently. Only EQP earned on AA-coded flights work nowadays. This changed about four months ago. For qualifying for / retaining status the normal way, what you say is still correct.

I'm on a Krisflyer program. The miles earned on other star alliance partners do count toward the elite status. Once u are on the elite status, u can only get the extra 50% of the miles flew on SQ flights. On all other flights, u will just get the actual miles flew.

Welcome SimonsMiles

I see in your profile you are based in London, England. So it could be a smart move (i.e. a not too silly one) to consider European FFPs, just to maximize the benefits. In my opinion AA has a great FFP, but if you are not in the US you can not really use a few benefits like the upgrades.

My 2c could be to have a card each for OW, *S and ST. Which ones ?

OW
I could start BA but the TP trick is quite annoying and the BA/AA transatlatic problem is quite irritating. I could say, use the BA to reach a nice number where you can have a nice flight (e.g. 50K is UK to Hawaii R/T in Economy) and then switch to a common program... i.e. a program where you can place ALL the OW flights, for example the Finnair one, where yes, you can place all AA and all BA and all other OW flights. By the way are you aware of TESCO to BA point conversion ?

*A
No way, stay with the BMI Diamond Club (BD). Read a bit more about it in the proper forum and it's really a good program, always in my opinion... o/w at 50%, biz only 50% more, first at 100% more, cash and mile (^ ^ ). Try LHR-HKG with NZ in business and let me know. And go on with the DC credit card.

ST
Be calm, be seated, fasten your seatbelt... go for Alitalia Millemiglia. The reason is the minimum number of miles, 1200 ! Quite easy and very soon they could be wiped out or merged one to one in the M&M of Lufthansa or in the ST FB of AF/KL.

Hotels
Stay with Hilton Honors and go for Diamond. Diamond brute force... you always get a room, even for award... only exception only if the property just burned to ground. And with the double dip you can get 1000 BD miles per night (max 3000). It's a booster.
With 30K PC points you can have a wonderful 1 night stay at an IC... try Le Grand in Paris, perfect for a weekend. And be aware of the many promotion PC runs, like a lot of 10K bonuses and double points/miles. And to be sure just do the on-line survey on its main web page... 250 bonus miles. Marriott Reward is great also but you need to be at least Gold to start having real benefits & savings, their travel package award can be soo good, 235K MR points for e.g. 120K AA miles and 7 nights at any category 1-5 property. By the way are you aware of Marriott Reward to TESCO to BA point conversion ?

Be aware of any rule of deletion (usually after 3 years of idle time)

Enjoy

For oneworld, if you occasionally will be flying AA transatlantic and other times flying BA, neither of their programs is going to work out for you all that well. You'll have to dilute the miles regardless of which one you fly.

Assuming you don't care about getting upgrades, just about making all your RDMs qualify, you might even consider choosing to join one of the other OW programs such as LAN (LA) or Qantas (QF). Then your transatlantics would count to the same program regardless of whether you flew AA or BA. Or even a non-OW program like Alaska Air (AS), where both AA and BA earn miles. AS has a number of partners including some airlines not in any alliance and some Skyteam airlines like KL, DL, CO, NW. Not all of their partners earn status EQMs (BA does not, AA does) but it would be a single bucket for all your non-*A flying.

Drowning in miles? Seems barely a puddle.

(Well, somebody had to say it. Surprised no one beat me to it.)

Only half true. You earn AA miles on BA flights in Europe, and he can just fly to the USA on AA metal and will earn AA miles. I've flown to Europe 6 times and have recieved all my miles.

Yes, you can still sign up under my referral if you would like. You will just have to provide an alternate address when you sign up, which you can change back later on. PM me with your email address and I will refer you.

You can build elite status on United by flying with the Star Alliance partners. These being Air Canada, US Airways, and the like. BA and AA flights will not build any status on United. Also, with AAdvantage, you cannot fly to the USA on BA and recieve miles, but you recieve miles on BA in Europe. Just check the booking codes and choose the schedule that offers miles - many do not. All the info can be found on the AA website. ALso, there is a 10% off coupon ex-UK in the AA Coupon Wiki here on Flyertalk - it can be used for 10% off any flight from the UK to the USA on AA metal. Let me know if you have any more questions.

Did I say anything different?!? Please re-read my post.Europe is not transatlantic US-EU-US.

Since you already have several hotel program memberships, you could change the options in the ones you do not use enough to get hotel awards / status to give miles to the airline program of your choice instead.

One thing to consider is that if you have a program that just needs a few more points or miles to "top up" to a desired award or status threshhold, you may want to change the award options in your hotel program memberships to make that "top up".

Note that being a hotel program member with 0 hotel points can give you little perks when you check in, though not always. E.g. I got free breakfast coupons at a Hilton once. Also, being walked due to hotel overbooking may be a bit less likely for hotel program members than non-members.

In the future, check online to see you got credit for the flights before submitting them, and if you haven't rec'd credit, make photocopies.

In my opinion, the original poster is not drowning in miles.

The question asks about lounge access. Some responses addressed this.

Regarding the question that this person's travel patterns frequently change, perhaps Alaska Airlines Mileage Plan might be suitable if the goal is simply to collect miles in one program.

Alaska's program allows credits on flights of British Airways, Air France, KLM, American, Cathay Pacific, Qantas, Lan Chile, Northwest, Continental, Hawaiian, and probably some other small airlines. Some of these airlines are competitors and wouldn't give credit on their own ff programs (such as American, a oneworld carrier, doesn't give credit for flights on KLM, a Skyteam carrier.)

Traveled to LHR, Madrid and Seville this Christmas and last using regular miles. Traveled to St Thomas Presidents week last year and Christmas 3 years ago using regular miles. Name one other airline that would let you fly using ordinary miles during peak travel periods.

If you have a friend/contact in your accounts payable department, you may be able to get copies of your expense reports and the associated ticket numbers. I've had to do that after missing credit on a couple of flights.