THIS
People should stop trying to be nice at all cost or to troll a guy who might be wasting months of gameplay just to realise his class decision was a one big mistake. If certain class is boring and weak just say it. Even if it looks that one guy likes particular class lore/concept and you don't want ot discourage him for picking what he might consider to be optimal for him, you still should give him nothing but hard and reliable arguments.
Stuff like "well TK isn't the best tank but definitely has it's own place and can be fun to play" is just a sad troll (be it intended or not) :f
To sum up this flame thread with almost no input on what OP was asking:
TK is:
Boring to PvE
Boring to PvP
Heavily reliant on having a good party because he farms slow
Has little in terms of active and impactfull skills
Isn't wellcomed in most CP's / CLAN's who are planning to PvP and contest EPIC's one day
If you simply like the lore concept and want an elf fighter, choose:
SWS for the tankish/supportish purposes
SR - if you want range fighter
PW - if you want a melee dpser (although he's arguably weakest of the daggers)
If you like the concept of tanks and want to be annoying to enemies, choose:
DA - Arguably strongest tank, that farms fastest, has reasonable ammount of DPS (due to having a summon), is tankiest of em all and will be a beast in the future Olympiad games
SK - Arguably most fun to play of all the tanks, a lot of active abilities/nukes, highest autoattack DPS of all tanks and interesting skillset (but is least tanky) and his general PvP power is below DA
Paladin - currently crap which might become a powerfull and fun to play TANK in the future chronicles
if you simply want to be tanky and not really perform as a typical tank you can consider as well:
Warlord - with +con dyes he's a very tanky class, with awesome farming potential, wellcomed in most fighter parties, who brings quite a lot of fun when fighting in the mass PvPs, but to play efficiently you need a dedicated recharger and after you run out of mana (what happens fast) can't do much more than simply tickle enemies with bow
Destroyer - naturally tanky hero who can become almost immune to physical dmg for 1.5 minute (GUTS), high DPS and decent for solo farming, he's main weakness is that he has no range abilities and can be very boring to PvP with