I recently went through a similar situation. I purchased an '06 Grizz this past April and I looked at almost every ute quad in the 500 - 800cc range. For me, it came down to what I felt most comfortable on, which was the Grizz. I am not biased towards any brand and I looked at all the features and how the quad was set up. Some people say a Grizz feels tippy. I would have to agree somewhat. It feels a little tippy with the stock tires on but you get used to it. I put wider tires/rims on and it felt a lot better. (See my pics) My bro-in-law has an '04 Grizz and he has 27" Dirt Devils on the stock rims and he hasn't had a problem with it being tippy and he's had no power loss. I can't state any opinions on the AC or the BF650 as I haven't ridden either. My other bro-in-law has an AC and he really likes it. I guess my opinion is that you should go sit on the three quads you're looking at and drive them and see which one you're most comfortable with.

HTH