Templars are apt for surviving, but tend to have problems keeping aggro. Warriors easily gain HP and Defense, Knight has an advantage for physical resistance and Eva, and Templar has a lead on elemental resistance. Whatever one class does not specialize in, resources go into covering other areas, though defense and HP are debatable about how much you need. Block caps at 50% and affects all incoming attacks. Eva caps at 100%, but you don't need 100% base Eva; procs for Eva and Agi bump it up easily. You always want to have Block capped, and you can get decent amounts of Resistances from crafting armor for Legendary Achievements. HP and Defense is pretty much: get it as high as you can when you're done with other stats. Normal damage reduction caps at 70% from Defense, but Crit Dmg reduction will never feasibly be capped.
Your gear has a larger impact on your tanking stats than your class. Can Knight max Eva easily? Of course. Can Warrior and Templar max Eva as well? Yes. Block? All of them can and need it. Defense? Sure, fortify armor. HP? KP, class expertise, legendary achievemens, pets, buffs . . . you'll have enough. Like I said, each class maxes something more easily, but needs to allocate resources into covering weak points, so it sort of evens up. Knight has only a small lead on physical resist, and Templar can get up to 10% elemental resist from KP. By the way, resists are very reliable forms of damage reduction. Eva gives a chance of avoiding all damage, but resists just make you very bulky so that you can afford to take hits. I consider Eva secondary to resists, but as a tank, Eva does not always come at the expense of resists, so you *can* have a decent balance between them.
Offensively, Templar is unique. It has amazing burst damage with its Knockdown, but long cooldowns seem to hamper it from generating a consistent damage output. Damage translates directly into aggro, so that's why people are suggesting that you fortify a powerful mace; you need tons of damage from fewer hits to keep aggro as Templar. Knight has a large AoE that has DoT while it cools down, increased aggro generation, and faster cooldown all in one skill. Warrior might lose aggro, but Group Provoke is an insanely large AoE that automatically rips mobs' attention from your allies to you. Templar has only a a Knockdown (which increases damage done immediately thereafter by 50%, making the difference between your damage and that of a true dps that much larger, causing aggro loss that much faster) that is very slow to cool down and a damage attack that does increase aggro, but has no other effect and cools down too slow to compensate for this. That means every point of damage counts.
To help keep aggro, try to stack elemental damage enchants and effects from weapons, armor, trophies, and enchants (and maybe ask a friendly Mage to keep Element Guardian up on you). For every stack of elemental damage you have on you, the aggro increase from Declaration of Anger is multiplied by that number +1 (since it also increases aggro generation from your main attack). For example, you use Declaration of Anger and you have one elemental damage effect. Its effect is doubled by being applied once to your attack and once to the elemental damage. If you have two types of elemental damage, it is tripled, and so on, so forth. On a side note, if you tank as Templar, it is recommended that you have all 5 points of +4% Malice on KP, and max out the KP of all talents that increases the damage done by your individual skills. Your defensive stats can be maxed mostly without bolstering through KP, but your damage and HP need to be as high as possible to keep aggro (and just because HP is a stat that more is always welcome).
That's my take on Templar, and here's a sample of what my KP would look like had I not messed it up with nubby placement earlier on.