i've ran all three the Alpine's are a different animal as the Chinnook and Timberline are more comparable.
Alpine - No DWR, Lightweight for warmer temps, Thin waterproof knee pad, Run big so size down, Nice warm weather pant
Chinnook - DWR but not super DWR it does tend to wet out faster than other DWR material such as on the Guides, light fleece backer for added warmth, Knee pads are same as Alpine very light and not cumbersome, Very good all around pant for cooler temps, hip vents will allow you to stretch the range some. I prefer these over the Guide pants as they are more versatile.
Timberline - DWR dries super fast, nice stretchy material that is not fleece backed just has a somewhat thicker feel to it. waterproof knee and butt areas with thick durable material, Knee pads are foam and removable which is a bonus, Comes with suspenders which are removable, No Hip vents which is disappointing but it does breathe well and is a versatile pant for around 60 degrees or less. i like to think of them as Attack pants on steroids.
Lately i have been leaning more and more towards the timberlines as my go to all around pants over the Chinooks for this group of pants. I like the fact that the timberlines are offered in solids and have removable knee pads. These three all have their own place and purpose but i tend to wear pieces that are more versatile.
Josh