Sejuani is really fun top, and oftentimes totally unexpected. Slap some Movespeed Quints on her and you can start roaming early, too! After her slight buffs, she a good pick for top (if not a tad OP in many cases - don't say that too loud, tho!). I've gotten numerous triples and a couple quadras playing her top - she's pretty easy to get fed (with a few ganks) and she's very useful, overall, to the team.
Alternative choices:
Pretty easy build, pretty fun to play, next to impossible to kill if you get even a little feed.
Very fun to play, very tanky potential while still being able to dish some steady damage. Only major con is his mana costs - very intensive.
Tanky, decent sustain, great team potential/team utility, matches your playstyle, I'd say.
SUPER fun to play. Pretty easy to learn but has a fairly high skill ceiling (many will argue, but trust me). I've had a lot of experience on Singed - I've won against duotops, and won numerous 3v1s as Singed, just need a lot of practice. Can be built supertank or AP damage. Iterating: SUPER FUN.
Matches your tank/damage style. His W lets you get HP just for killing things - what fun :P Tons of utility: Slow, (aoe) knockup, shield, a semi-global ult that makes him faster than Rammus, passive that lets you come back after dying briefly with insane damage...pretty fun overall.
ALTERNATIVE OPTION TO CONSIDER:
Now, this isn't your playstyle listed, but I main Quinn top and it's highly viable/successful. Takes a little while to get used to, BUT, she has a really additictively fun kit to play, great carry potential (hypercarry, sometimes - I've went 18/0/15 with her top), and amazing post 6 roaming potential. You can solo drag for your team, and can get across the map to that teamfight after you just splitpushed another lane in almost no time.