Templar because they can heal well.
People say their damage isn't great, but they shouldn't make that a statement because it's not considering all the factors.
It's obviously about balance. If they had the best DPS + best healing wouldn't it be out of balance with other classes?
And even then you don't notice the differences until you get into higher levels.
I can put a Templar next to a Shaman for example. Sure the Shaman can out damage, but only by a margin. And consider a bot situation where you aggroed three MOB (at above or about the same level) at once. The odds are more the Shaman will die, because he has only limited heals. It has two HOTs, and at around lev 30 you can use a heal totem (slow cast time). But the Templar will have three heals and a HOT as well at the same level.
I use a shield/wand templar, don't know how a staff one would fair..
Also have to factor the balance with any class, if you you can kill the monster fast you need less healing..
And Defender if you equip one with a dual handed weapon are good solo bot chars.
With such high defense they can take a beating with less down time for healing.
And do decent damage really, if you have a two handed weapon it only takes so many hits to take MOBs down to nothing.
I tried a defender where he can solo bot MOBs +5 levels with little problem.
They get a small HOT around lev 30, but it's only limited help (at least with one point) since it's pretty small.
Notice in most games the Chinese farmers use melee chars for a reason..