I'm still a virgin, and my first couple toys, a vibe and a glass dildo, were both one inch in diameter.
Now my preferred dildo is a silicone one that is one and a half inches in diameter. And for me personally, that one point five inches is a snug fit. I find it leaves me feeling quite full. I have no desire to try accommodating anything larger, at least in terms of toys.
Either way, I suggest that everyone starts on the smaller end and work their way up. Otherwise you might bite off more than you can choose, and end up wasting money on a dildo you never use.