Not sure about Ubers (particularly solo) for which you will likely need “1337” gear for a Smiter build, but I can personally attest that the Fist of Heavens (FoH) Paladin is a very strong build once you hit level 30 and get access to that skill. Basically when you hit level 30 you alternate putting skill points into Conviction, Fist of the Heavens, Redemption (very important for mana), Holy Bolt and Holy Shield (the latter so you have some reasonable blocking to compensate for your low defence factor).
Almost any Mercenary works with this build, although I prefer A1 Cold Arrow Rogues and A5 Frenzy Barbarians.
The big challenge is that you have to play a melee Paladin (e.g. Holy Fire) prior to that, which means taking on normal Diablo in melee – make sure your fire and lightening resists are as high as you can get them, and be ready to run a lot!
Good luck!