Totally depends on the person and what you'll be doing with it. For me, I like the big, wide ones but others may like something different. For whatever reason, I prefer large anal toys. The small ones aren't any fun for me. BIG BIG BIG!!!
I really like silicone 1 1/4 " plugs they fit me really nice and give me the stimulation I like sometimes I go to 1 1/2 " plugs for a more filling feeling. Plus I can get 2 silicone plugs for less than half of the steel plugs, for me it's a no brainer 2 for 1/2 the price of steel