I have all 3 that have been discussed(Mountain, Timberline, Attack). As others have stated the Mountain and the Attack are a bit closer in resemblance, but not entirely. the Mountain Pants are the lightest of the 3, they do have knee pads which are removable which is a plus, but they don't have the hip vents for dumping heat in hot temps. Between the Mountain and the Attacks i prefer the Attacks as they seem to be the most versatile in regards to the temps you can cover in them. The Attacks for me are the perfect balance of what i'm looking for out of a hunting pant. Now the Timberlines however are a completely different animal. They are certainly not a hot weather pant but can get you though just about any season you need them to. The waterproof butt and knee areas are essential and top that off with removable knee pads gives it a ton of versatility. All 3 pants have a nice stretchy DWR fabric that dries fairly quickly. If i had to chose i would primarily run the Attacks and Timberlines and scratch the Mountain pant as i could easily get by without it. In a perfect world someone would put hip vents in the Timberlines and never look back as it would be king of all hunting pants!
Josh