Around here any way, it's the 46 or husky equivalent.
The 44 will handle most anything anymore. But, the 46 will do it more handily and with a bit more snap should you needed, which often times you do.
The 66 and up are nice good saws but the draw back for me is the killer, they start getting heavy. Draggin that thing up and down all day gets to bugging my elbow and shoulder at times. Don't get me wrong I like the 66 and hope for a stand that it would be 32"+ stumps but that is getting fewer and farther between these days. Follow the rule of "power", you can't ever have enough. If I had a Slinger 66 that would be my go to saw with out a doubt, but I think I would rather have a 46 that he had tinkered with. The 66 will last longer because it won't work as hard that is the other side of that coin. And it will just get with it when you need it to. It's also fun to use at times when you are just out having a good time and the pressure is off, or when you are batting clean up after a bad situation.
Have you made you choice yet?