For the most part, the leagues I'm in do commissioner approval. It's much quicker, and there usually aren't that many trades that need to be vetoed anyway. Usually if the commissioner is involved in the trade, someone else makes the decision on the trade.
Doing a league vote is usually only possible if you either have a very active set of managers or set a reasonable time limit for putting a vote in. I'm a bigger fan of commish approval because it's quicker, and if a questionable trade comes up, the commish can always ask for opinions from the league on trades.
Kudos to Leber
for the amazing sig and to Metroid
for the userbar and making them both fit
2008 and 2009 Defunct Dynasty League Champion