A well developed, fully equiped Hammerdin is by far the most capable single character in the Diablo game. There are other characters that in combination out perform a solo Hammerdin in PvM (Player vs. Monster). However, for single character to single character, the Hammerdin is the top killer in the game.
A Zealot uses the Zeal skill as the primary attack skill. As you can see in the graphic to the right, the Zealot has multiple strikes (5 per turn) with enhanced damage and enhanced attack rating. Enhance Zeal with the Fanaticism aura and the damage and attack rating is very high.
A Group Pally will add tanking and a great aura to the party. The Fanaticism aura will increate the damage of the Necro's skellies, the Shapeshifter's Bear, all mercs, and all players. It is a fine thing.