When I ride English, I use the cheap ones: Pro-Craft Stirrup Irons Pair - Statelinetack.com
I've tried 4 bar stirrups and hated them. I tried plastic ones and they hung up on my rubber soled cowboy boot (OK, I'm not quite a traditional English rider). Liked their weight, but when I pulled my right leg up and the stirrup came with it, I decided it was a no-go.
I could be tempted by these: Korsteel Flex II Stirrup Irons - Statelinetack.com
But I honestly think the best bet for most riding is just your plain, ordinary el-cheapo stirrup. I sometimes have taken the rubber pad out of them, but my riding now is done with leather soled cowboy boots, and leather against steel doesn't have enough grip. If I use riding shoes, then I prefer the rubber sole against the plain steel.