An upgraded guardian angel is nice as the defense goes up to about 1250. But then the strength req is very high (196). If you can use this feasibly with your build socket it with an um too and combined with an um'ed / pdiamond zaka you've got great resists.
My hammerdin's using stone at the moment for high defense and resists and have no probs at all with it. Can't afford enigma yet but imagine that would be a lot better.
Also depends on what you're facing. Zealot dueling is all about AR and defense. Pretty much whoever hits the most wins, so you'd want a 1700+ def fort, a 2k+ def stone, or an eth steel carapace. If you're killing casters, you'll want an um'd guardian angel with supplimented resists to get all your res up to max. Keep in mind that if you also put 10 pts in each resist aura, you'll have 95% resist all, spare poison. I have to agree that coh is my favorite though, with +2 skills, 65 res all, 8% pdr, and a bunch of other nice mods for pvm. It does tend to be expensive to repair tho. If that becomes a problem, eth carapace is gonna be your best bet since it autorepairs and won't show up on your repair bill since it's eth.
To date I've never made a Paladin. But my brother plays them quite often, and his current Paladin used a Fortitude for some time, but he recently got a Templar's Might. Some of his past Paladins used Guardian Angel/Shaftstop.