Depends on what you are going to be doing with it. Look at some of the "Moon Buggys" they have small engines. The one that Jon from A-P comped years ago had an air-cooled VW engine. If you are talking Toyota 20/22r or the newer 4's that come in the Tacos they have good HP and lots of torque, 3.4 V-6 is another.
You can ask this question to 15 people and you will get 15 different answers, just like all motorsports.
