i stay away from team games, so this is just for solo's:
i almost always get warden first (unless for no reason i feel like something else, usually DH or kotg, never, EVER potm) and get SS to keep their harassing to a minimum. i tend to go SS, FoK x 2, blink, SS, vengeance, but i'm sure there are better builds. all i'm gonna say about a 1v1 between warden and DH is this: it would only happen in very early game situations (and only in solo games) and almost always in one person's base. no matter what race you are, being in your base will be hugely advantageous, most likely giving you the win. if for some reason you're not, the warden would SS, whether it got mana burned or not, and the DH would most likely spam mana burn (i've seen some get immolation as first skill). the DH would probably win the 1v1 at that point. but like i said before, this would only happen very early in the game when your hero is still level 1 and you can revive him/her as fast as you can train a damn archer.
during the late game, i would probably choose warden over DH. sure, metamorphosis is sexy as hell, but whenever i see that i instantly focus fire everything on it. that either makes it die or effectively useless as it runs around in circles. on the other hand, vengeance avatar could make all those beautiful little invulnerable mini-me's, often adding 10+ to your army. the avatar is much more versatile in a battle because you can make it dance around while still having use of your hero, and it only needs to pause for a moment to raise a mini-me.
but that's just me in 1v1's. big chance i'm probably wrong, and i'm still playing on the level where everyone has only a mediocre micro.