Oh boy, mine is/was a Doc Johnson black silicone plug. It is either an inch at its widest point or a little under. It was the smallest thing I could find to start experimting with anal play. I've since gifted it to my partner.
Next was a medium sized red Doc Johnson silicone plug. This one is a little under an inch and a quarter at its widest point.
After those two, I started picking up the good stuff for our butts. That's when I picked up my first N'joy plug.
Since then we've, well I, have all sorts of vibrating and non vibrating toys.