There are a long list of viable Pokemon that fit both of your requests, but the one best suited for your team is more dependent on your team itself and the Pokemon it will be working with. For a list of options, you should probably check out Gen VI OU forums, where people discuss OU Pokemon of all different types and roles. I'm sure you'll be able to find what you're looking for over in that forum.
I'm no lower tier expert but I can say that Seismitoed's role should play a bigger part in helping you determine its set than what is standard. If you like the Assault Vest defensive boost, then you're probably better off running a bulkier set with more defensive EVs, as you know you're inclined to play it defensively. In terms of the ability, again it depends on how you play it. Obviously, if you choose to go special, water absorb is the answer, as without contact moves Toed can't take advantage of Poison Touch. In general I'd say Water Absorb is also better on a physical set, but I guess Poison Touch could be interesting to cripple walls.
If you are looking to be standard, you should probably run Special, or you can check out the Seismitoed analysis that's on site right now for a general idea.