I use for bass the same ones I use for trout. Think they're 2mm and rated to 15lbs. My tippet is generally less than that so in my opinion there's no real need to have a heavier ring. For carp though, might consider going up a size for the tippet ring, but really only if your tippet is going to be rated higher than the rating of the tippet ring. And frankly as I think about it, for just bass and carp fishing subsurface, you could probably just use a swivel or split ring for a lot less money if you just want the luxury of changing tippet without having your leader get shorter over time.
As with knots on the leader, the one downside to any of the options above is that it's one more thing on the leader to snag weeds, etc.