Alamo typically has the longest lines because as the official rental car company of WDW, anyone who gets a rental through WDW Reservations gets one at Alamo.
I don't have any complaints about Alamo. I used the self-serve kiosk back in June, and plan on using it again in December. And who can beat $85 for a Compact for a week? (That's *with* taxes and fees, after my wholesale club discount and a coupon available on the Alamo website)
I'd do online check-in, but I think I'm ineligible for that because of the group discount code, so I have to use the kiosk or stand in line.
-Rob