Anything but Selene's, the only people who get hit by the bear are potatoes.
Unless you are willing to be a mindless sycophant and/or coddle others due to their insecurities prepare to be harrased by the Orwellian enforcers on these forums. You should also try to refrain from using any words more complex than those used by a small child due to the fact that said enforcers have made it clear that their vocabulary pool is aenemic.
Which is a better option in your opinion for a Stam Warden? And why? (Pvp)
Not playing a stam warden, but I would still recommend velidreth for PVP in general. Simple reason beeing the option to utilize velidreth when not within melee range (proccing of any damage) and hitting (any) target even in fast paced combat situations (due to the spores actually moving untill they hit).
Selene may hit harder, but it requires your target to be stuck in place for the proc to hit and it requires you to use direct melee damage... both can#t be guaranteed in PVP. In PVE, and with a melee char i would always favur selene over velidreth... in PVP thats different.
Selenes will only hit people in PvP if they are stunned, knocked down, on fire, having a stroke, suffering 999+ ping and a potato....all at the same time..so..I wouldn't bother birning it anywhere near the pvp space.