In act1 i made a point of fighting ALL neutral critters.... extra XP... from act 2 onwards i chose which ones i wanted to fight....
Tibars i NEVER fought... its too painful to chase them constantly...
Stone biters i never fought.... that beserk spell got the better of me more than a few times.... so i left them alone....
I normally chose the creatures that was NOT 8 levels weaker than me.... so that i can get XP... if not, i stayed friendly to them.
Since i played hardcore most of the time, getting XP was vital for me especially in the beginning.