Yamaha, hands down! The 150 is one of Yamaha's better engines, the local boat taxi put over 5000 hours on their 150s, when they sold them, I checked compression and leak down, they were still within spec of new. The Honda doesn't have that good of a reputation around here. parts are expensive, and they corrode pretty bad. Weight is pretty close to the same for each (480 lbs). The Yamaha is a pretty strong 150 as well, supposedly making close to 165 hp. It may come down to which dealer you like.
http://m.marine.honda.com/outboards/motor-detail/BF150
http://www.yamahaoutboards.com/outbo...specifications