No, don't go for the AA miles. They are worthless.
I tried searching about 7 different destinations a couple days ago for flexible days within 1 week periods for several different weeks next year and only 1, I repeat 1 had award redemption available at the lowest mileage rate. And with that, you had to make 2 inconvenient stops and overnight in ATL to get there.
You will not find that with UA. 80%+ of the time, you will be able to find the a reward at the lowest redemption level.
AA reward system is unacceptable and nearly impossible to use. If only 1 out of 7 destinations on multiple dates qualifies for the lowest mileage redemption, there is a problem.
Second, don't even try booking to Europe. I haven't managed to find 1 ticket yet that doesn't route you on BA, which rapes you in fees. The reward ticket will cost between $500-700.
So, yes, United does have the best reward availability by far of the USA Legacy carriers.
I'd like to fly AA more and accumulate more miles, but with an inferior card and award redemption's, I simply will not be changing programs.
Thanks!