Mk wins the game 1 on 1 any hero, repeatly stunning you with bash, then repeatly bolting you, then slowing your attack/movment with clap, while you can only normal attack him because he'd be in avatar.
he can own the warden even if she does blink away considering bolt does like 300 and a quarter of the time your stunned using about 100 life every 2 seconds from his normal attack.
and mentioning blink is just stupid because any hero can be cheap, but any legit 1 on 1 hero battle, mk would win.
for the best hero for melee i would have to say DL because ofsleep which will get your tier 3's or your hero/infernal to get OBLITERATE those casters and carrion swarm most of the time for lined up units. and with vamp aura, hes unstoppable

but tc is equally good because he will stay alive
the best harrassing hero would be either bm for being annoying and singlely frustrating your hero, or fs. i would say fs because of wolves which would be the equivalent of 2 footmen and later on maybe a tier 1 grunt. bm in the beginning owns but eventually the other dude gets detectable stuff and your bm will get his ass handed to him. but fs on the other hand lives because he's range and 'he doesnt die.
the most useful hero would be AM because of bril aura, AOE spell, water element. WE does like 45 dmg at level 3 and has a lot of health good for air and would kick gargoyles/hunts asses. bliz will own casters/range and bril aura is just amzing with mana. and dont even get me started with mass teleport =DDDDD
my favorite hero is dark ranger cuz of silence and charm, silence wins tEh game and charm can get any unit even air

(except level6creeps) and she wont die with life drain.