The 2.7 is nice, and adequate. The 3.4 is nicer, and more adequate. Mileage is not significantly different between them, and the 3.4 timing belt is easier to change, if more often required (90K miles, though I understand the newer designs' service interval is 120K. Check with your dealer). Since the water pump often is near its life at the same time though, you would be in there anyway to change it, so something to consider.

-Bill
'87 4Runner w/ '96 5VZ-FE, 'Red Chili II'
'97 Taco XtraCab 3RZ-FE, 'BlackBean'
TLCA # 13257, Rising Sun 4x4 Club Land Use Coordinator
"He who stops being better stops being good." -Oliver Cromwell