I've done Turtle Island (site32 is great) and Big Burnt so far. I only "discovered" Lake George a few years ago but I am trying to make up for lost time. The islands with single sites look awesome; I mean, how great is it to have your own island on such a wonderful lake? Accordingly, the reservations are booked far into the future for those little islands.
I've found the staff at the ranger station on Glen Island to be very friendly and helpful. Tell them what you are looking for, eg lots of sun, views, etc. and they will recommend specific sites.