I've tried bullets/eggs, non-animal rabbit-type vibes, traditional, vibrating cock ring, and g-spot vibes.
My favorite for solo use is the bullet/egg. It's just very versatile: great for all-over body play. My very first sex toy was a double bullet from Doc Johnson, and even though it got dangerously hot toward the end of its run, it serviced me incredibly well.
Favorite for partnered use... Probably the vibrating cock ring. I did have to be on top for it, and that position is not my favorite, but I was compensated with a vibrating boyfriend and man, was that AWESOME!