Left Delta and my lifetime Crown room membership for AA and never looked back. Never a problem cashing in miles for flights - this year over 300,000 miles converted to great use - Delta -almost impossible. All miles count towards gold,plat or EXP. EXP program is the finest - just read the comments on the AA board.
OK...I still fly Delta to a few markets - upgrades - impossible, attitude - impossible. I'm happy I live in a market where there are airline choices. :-)