I have LT PLT on AA, and because of my AMEX PLT, now have CX G.
Should I try and credit to another program now, so I can have status on multiple airlines?

And, if so, which one?

DL with Skypesos, I can't count on their value being able to last.
UA has way too many elites.
A3 has a good entry rate for *G, but their redemption rates aren't the best.
KE lounge in ICN has been very crowded at times (even more so than an AC MLL in YYZ)

Depends how many miles you're flying a year, and whether you intend to retain status on an additional carrier. Are you going to retain EXP at AA, Gold at CX (what is that in One World hierarchy?), and then top tier at someone else? Are you flying 300,000 miles a year?

It doesn't make sense to scatter low and mid-tier memberships around different alliances when the best benefits are at top tier.

I have LT PLT because I have 3.7 million PTD miles. My CX Gold is because of my AMEX.
I fly 125K miles/yr, but I do find price to be a growing factor rather than loyalty when flying.
CX Gold=OW Sapphire.

I'd focus 100K of that flying on whoever gives you the best perks at that level, including award travel. Are you looking at leaving EXP behind, then, and just falling back on Platinum?

For instance, UA at 100K requires you buy up to an upgradable fare to use systemwides on international travel, while AA does not. If you want to fly places AA does not go, and have a chance at upgrades, you should look at 1K at UA. Just keep in mind that some of those upgradable fares can run $700 higher (like SFO-SIN), and there's no guarantee, or refund, if you don't clear. Not everything is grand over at UA.

I'm leaving UA this year (did my last paid flight with them last weekend to IAD) because I don't like the changes to mid-tier and lifetime status there.

How about award redemptions at DL? I've seen occasional complaints that reasonably priced award travel can be a challenge there? Have you checked the Delta forum to see if that is still the case? No sense in building up miles you can't use.

It still is on DL.
I think that AA focuses too much on connections via LHR to Europe, the Middle East, and Africa, and too much on NRT/HKG for places in Asia.
On the other hand, I think that I like how easy it is to use SWU's at AA.

Star sounds like an easy option to me, as A3 would allow me to obtain status easily (and they have lots of bonus miles with certain fare classes.)

But, with Skyteam, KE has better availability for award travel, but still not the best rates.

I agree with much of this, particularly looking to accumulate 100K on an airline. The perks, including treatment in the event of irregular operations, are much better if you have such status rather than spreading your mileage accrual around.

AA is definitely the best FF program, with UA deteriorating in ways that even go beyond the problems tom911 has identified. AA upgrades with SWUs at time of booking are much better than at UA, and it is generally better in terms of many mileage redemption options than UA is---and much much better than DL is, AFAIK.

Still, if it's routes and going through LHR are problems for you, then I'd suggest UA over DL.

Yes and no. I am flying directly from ORD to Abu Dhabi next week on Etihad. I have recently been "cheating" on AA and have attained 1K on UA as well. My very short experience on both airlines suggests that AA is where I will continue to focus my efforts next year. Between BA, CX, JAL, and Etihad, the One World grouping of airlines is IMHO the best out there. I agree that Asia can be annoying and that is where I tend to wander over to the *A.