If I have to pick one favorite, it's blue cheese/roquefort. However, obviously on a Cesar salad I want Cesar dressing- otherwise, why call it a Cesar salad? I also like Thousand Island (Pink Sauce as the no-longer-Resident 8 year old calls it), and I also like Green Goddess (which we grew up eating in the 70s). I am not a huge fan of Italian dressing, but I use a lot of Ken's low-fat Italian as marinade for chicken.
I do NOT like ranch, in any way, shape, or form. I also try to avoid balsamic, as it makes my tongue very sore and somewhat swollen, although I can eat balsamic if it's been used as a marinade and then the food is cooked. Must be some sort of enzyme in there.