Thunderroad- Thank you alot for your input!

to clarify- I will be flying economy, and no, I didnt know that I'll be getting less miles for flying on cheapest economy. Oh, well, I guess, thats' all I can afford right now.
And thanks to FT I will be steering away from Delta. I did check out the spg site for tranfer rate, US and AA looks good with 1:1 transfer rate. However, from what I understand reading FT, US is really hard to redeem miles on.
I've read about a possibility of using US miles to get an award on Star Alliance partners, I dont know how good of a deal that would be, or if it'd be better idea than AA.
So, please any more advice is welcome!