Elyos templars will be the better templars for damage and survivability. To start with, lets compare end game super skills:
Elyos:
Nezakan?s Shield I - Skills - Aion
Asmo:
Zikel's Shield I - Skills - Aion
Now compare. Same except the last part. Would you return a fraction of the damage you take, or take no physical damage period? In mass pvp, returning a fraction of 30 people beating on you will leave you dead in seconds. Taking none for a while will leave you alive.
Let's go lower, to the bigger point. In Aion, DoT's are useless. We have plenty of skills, abilities and pots to get rid of debuffs. At lvl 42 we get an amazing attack skill. Now compare:
Elyos:
Brandish Shield I - Skills - Aion
Asmo:
Slash Artery I - Skills - Aion
The asmo one is very low damage with a bleed skill. The bleed skill is a DoT that only retards suffer. Anyone with a brain removes it instantly. And even when not removed, the bleed DoT is low low damage. 1 HoT pot heals more than you'll lose. Now for the elyos one, it requires a shield block, but it is a massive damaging skill upon a counter. I've seen some lvl 45 templars use it for massive crits against assassins, glads, etc. And theres no pot to resist it or remove it, it's 1 big massive shield smash.
Elyos is more "Tank" and more "Direct damage slams" while asmo is more "reflecting" and "DoT's". Best i can compare would be templar to be like a holy knight thing and asmo to be a dark knight thing. Elyos is "The power of christ compells you...and my boot right up your a...!". While asmo is more "I like stabbing people from behind. Partly because it means i don't get hit, and partly because we asmo like being behind other men."
You decide, righteous right hand of god! or you use your right hand for reach-arounds on other asmo men.