AApoke strongly advises NOT to join OnePass which is Continental's ff program. Keep in mind that there may be some people who are very satisfied with OnePass. I am one of them. Each program has its advantages and disadvantages. Check them all out and go with the one that best suits you.

I think the best advice is to sign up with them all. You will most likely go with an airline naturally (more flights, cheaper, better connections). But if you find a good deal on one airline that is not your main airline, you can still earn miles.

I have AA as my main and UA and CO as my back-ups. Sometimes my flights have to go on one of the back-ups and as least I know I am still getting miles even if not the status

I'd say check the routes on the airlines you're interested in.

I really think that for southern California and flying "light," it's going to be United and WN. ;)

While not applicable for the OP's traveling habits, UA does sell access into E+ for an annual fee now.

I agree. Join them all, get an AA and UA credit card if you're interested, and just fly what's most convienent until you get preferences.

As another So Cal resident, I second the notion to go with AA. Their EXP desk is great and the ability to use the Starwood AMEX card to get the extra 5K bonus as stated above is really a plus. Also, I fly to JFK quite a bit and AA schedule is very convenient....

Sign up for every program you might possibly be interested in. Pick your first few flights by schedules and fares. You'll soon see a pattern. Focus on whichever airline it is.

Don't get an affinity card until you've picked an airline. Get a Starwood AmEx, which (as noted earlier) lets you transfer your points to whichever program you end up with down the road. You also need Visa/MC for places that don't take AmEx. If you can afford $95 and think you'll use it enough to justify the fee, get a Diners Club card. It's accepted everywhere MC is and you can also transfer its points to just about any airline program. (If you go this route, find a DC member to refer you. It gets him/her a thousand points or so for the referral and it has no downside to anyone. Many FTers would volunteer to serve if you don't know one already.)

Thank you all for all the info.

I think I started to get an idea how it all works. A long way to go though.

I notice that “starwood from AmEx” is very popular.
Doing my research I found that “Preferred Reward green card” from Amex also allows to transfer point 1 to 1 to 11 FF programs. Which is as flexible as Starwood card. It also gets you 2point per $1 is gas stations, supermarkets, drugstore. Of course it has a hefty fee of $110. but nobody seems to mention, this card on the forum. Is it not popular because of the fee or some other reasons?

Thank you

If you spend $20,000 per year on the Starwood card, you will end up with 25,000 miles when transferring to most airlines. If you spend $20,000 per year on the "Preferred Reward green card", and want 25,000 miles, $5,000 of the $20,000 would need to be at gas stations, supermarkets, and drugstores, or around $100/week. Discount stores like Costco, Sam's, and BJ's don't count, even if you are buying gas, groceries, or drugs. Neither do Walmart, Target, etc.
In addition, some people find that the Starwood points are more valuable used to get hotel rooms at Starwood properties, so they never convert them to miles.
Some FT'ers are single and travel heavily. This cuts down on their CC usage for gas, groceries, and drugs, and they put a lot of charges on their cards for airfare, hotels, car rentals, and restaurants. Your situation may be entirely different, so you will have to evaluate which card is best for you, not for some other poster.