Welcome.

The Wiki has a nice ability to compare two frequent flier programs, you might want to play with that a bit.

The advice I've heard from others that rings true for me is this: Don't try for status on a second FF program until at least you've acheived top tier on the first. So if you can do top tier on both US and AA, it might be worth considering, otherwise you're going to end up frustrated by mid-tier or worse on both.

AA probably won't match your US status (the only way would be if your company does a lot of business with them, then it would be arranged through your corporate travel dept.) They will let you do a challenge, sounds like you've started to read up on those. The Wiki is a great source. Be aware: 1) You can't challenge to EXP, only PLT. 2) You're nobody until you complete the challenge (can you say 31E?). 3) You won't get free upgrades as a PLT, only once you've reached EXP (100k EQMs, EQPs or 100 segments). 4) The strong advice around here is don't challenge to a level you don't plan on maintaining, lots of reasons for that.

So... assuming you can't get to top tier on both programs, you need to choose between the two. AA, AAdvantage and particularly the ACs are great.

Some things you might miss if you switch: 1) Free upgrades (until you make it to EXP) 2) Upgrades on partner airlines (AA/AAdvantage miles will get you none, zero, zilch) 3) Only BIS miles count towards Elite status.

Some things you'll be glad for if you switch: 1) Lots of lounge access all over the world once you make PLT. 2) Really helpful AAngels at the ACs. 3) Powerports on almost all the mainline planes.

I'd spend some time looking at schedules on the routes you fly for the two airlines as well.

I hope this helps.