My main is a human lk but I have leveled all lk-eligiblelasses to at least 15. The only real differee is the rials. For arena I would lean more towards O only
bc they have +5 dmg from pets. Now if you plan on doing both it reallyomes down to what you want to look at for 70+ levels. And all lksan fear.
If your gonna be PvPing, I'd probably pk Undead. Will of the Forsaken is extremely useful in PvP. However, pk what you enjoy the most. I think the Os get a bonus to thier pet's damage? That's probably useful. The silee and mana steal the BE getould probably be really ne in PvP too though.
If your spif goal is to rk in bgpvparena, go BE or Undead. That said, O's resist to stun is alose sond. It's generally useful (you never know when it will help you - you often don't even note it when it helps you). The other two rials: youanontrol. (and the o's +5% to pet does help - it does add up - but it's probably not as "huge" in terms of "turning a fight" - as the undead and BE rials reallyan be). Undead - having TWO ways tolk out of fear (and several other nasty effts) is quite powerful in pvpbgarena. BE - being able to area silee is very ne. Itan save you from a mage. Itan stop a Pal or other healer from saving himself or a friend -an keep you
from having to kill something "twe." Used w Felhunter, this gives you two silees. The only problem is that it's pretty short range, but this is offset by being an area efft. O, for a demonlk mostly doing pve, or mostlyoerned about leveling up, might be besthoe. In the long run, all res work. Go with what makes you happiest.