Tantus Ryder. med (which is really the only size commonly available). Can wear it 10hr no problem. Doesn't rub, doesn't ride up, has a nice tapered end. Not too big, not too small--you'll feel it, but nothing obnoxious. Never "falls out" regardless of whether you have anything holding it in... Tantus makes EXCELLENT quality toys---> silicone, well made, last a long time, worth the price.

Have heard njoy plugs work well too--but they are VERY expensive.