who is tankier, ranger or bard

[astrohax]

I know neither of these are necessarily strictly tanks, but i have a 28 ranger and thusfar tanking hasnt been that bad. I am not so much interested in warrior, paladin, or shadowknight, and the CC capabilities of the bard and ranger sound like interesting things to throw into the mix in a tanking situation. I have 2 friends that frequently play; one is dps the other healer, so I figure if i can at least be an offtank, we can always start a group.

Bard seems to be able to wear plate which is gonna amount to probably more ac, but do rangers have better max ac stats?

Is there a definitive answer to the question of who has better damage absorbing / mitigation potential. Also what are your experiences with these classes as taking on the role of tank/offtank.

any input is welcome!