As a guide these are things I consider when buying a new motor:
1. I can get a Mercury for very little $$, but I have to sell it every year because of their poor warranty. Yamaha costs more but gives me a 3 year warranty and will last me 5 years, about 2500 hours. So Yamaha is actually cheaper.
2. Service and maintenance is very important, so make sure there are dealers close buy that have parts when and where you need them.
3. To me one of the most important things to consider is a motors' re-sale value and used Yamahas are always in great demand.
4. Be sure you consider and compare the weight, if you pole in shallow water like I do it makes a huge difference.
5. Try to buy the smallest motor you can get away with, almost all the guides I know wish they had a smaller motor.
Good Luck, Mel