Improved Trip calls for CE which is another stat investment and tome as well as feat.
Stun is easier for barb to preq.
And as for stun... i recently leveled up 32 human barb without any alts help. And it was quite good, the kicker was early cleave and great cleave for all this moments when you are swarmed by kobolds/goblins/scelies/ogres. I dont really miss stun, till GH (got it at 12) but then pop the problem that when content is hard enought to stun matter it not always land - well life - maybe with dwarf or HO it will work better.