Just in general (not DL-specific), we like Alamo. They tend to have the best rates (we use our Entertainment card) and nice cars. We often get upgraded cars or free satellite radio w/ them. National is the same company, just usually slightly more expensive.
We've also rented from Thrifty w/o problems, but their vehicles tend to be no frills.
We rented from Enterprise in San Diego once... They tried really hard to get us to upgrade from the compact we had rented, then they gave us a car w/ the power steering shot. When we brought it right back (pulled out of the parking lot, realized we couldn't turn it and went straight back to them). They claimed that it was b/c we rented a compact 'compact cars don't come with power steering' they claimed. We got another car - one that would turn. Anyway, that was my one and only experience w/ Enterprise. I have no desire to deal w/ them ever again.