I always think I'd prefer standing starts, for several reasons. First off, I've never actually played a game with rolling starts (Okay, NFS:Carbon, but don't remind me, that awful game still gives me nightmares.) I always liked the standing starts in Forza 2 and 3, even if it did tend to lead to some pileups if the first corner was tight.
Second, I like standing starts because they test your ability to make a quick launch, just like playing with a manual setup to test your ability to utilize the car's gears. I enjoy trying to get a quick, barely-squealing start, although I don't think I've ever pulled a proper one off, as I'm not very good at it. I'll keep trying, though.
Lastly, standing starts show who's who in the run to first place, and, as well as showing which car is faster, also gives a clue as to who is the better at making a quick launch.
I'd prefer standing starts over rolling any day, although I'll have to try both to be sure. I don't find the cons mentioned about standing starts that much of a problem, that's all.
Oh yeah, and you can't set a time on the test track without a standing start, so I'll be practicing that a lot.