RE: best 300 or 400 atv and why?
A 300 is lighter, which is nice if you stick it. The 400 has more power, which is nice when moose/elk hunting, etc. I have a 400 Polaris Sportsman now, been good, except the starter is located on the bottom of the undercarraige and sometimes the seal will break and take on H20...making for burn out. They ain't cheap either. Other than that I love it, it easy to drive and has done the job.
Personally I would recommend a Honda, I had a 300 fourtrax and it was awesome, but a little lacking in power for the big stuff. I would look at the Honda in a 400. If your planning on moose hunting or hunt near bogs...put a good warn winch on it. If deer and hard terrain, you'll be ok without the winch.