I have only owned the Kuiu Attack pants so I am not much help there. But I have been using the Timberline pants the last two seasons and absolutely love them. The newer model is a little tighter in the ass end but not really an issue. The waterproof knees and seat hasn't failed me yet. I will not be changing my mid to late season pants anytime soon.
I've used the Kuiu Attack, Alpine, and Guide and only the Sitka Mountain pants but all accounts say the timberline is just a mountain pant with waterproof knees and butt. To me there is no comparison, the Kuiu Guide has better water resistance, is a bit thicker and the huge separator is the hip vents and also how the thigh pockets open and allow additional venting, then the normal pockets open in a way that allow more venting and if you are still hot drop the fly and you will feel a breeze blowing through the pants. The ability to vent seems like a minor or non impact feature but once you try pants that have that ability you will never go back. I can hunt through such a wide range of conditions and never have to stop and adjust clothing layers because I can just reach down and zip open or close the pant vents. I would put the Mountain/Timberline pants more in line with the Kuiu Attack for thickness but the Sitka pants don't breathe compared to the attack so they will be a little warmer when its cold and too miserably hot when its even warm not to mention hot. I tried the Mountain pants for two years in a row. Actually bought a pair and didn't like it then saw how much people liked them and thought I must be missing something so bought another pair and once again sold those. To me waterproof knees don't do much and neither does the seat really. If you are sitting and its wet or cold I have my sitting pad anyway otherwise you will cool down fast and get cold from heat loss through your butt. Unless its single digits to the teens I don't even wear long underwear with my guides thats how warm they are but at the same time I was more comfortable in 50-60 degree weather wearing them with vents open than Sitka Mountain pants.
I have the timberlines and they've been great. They cut the wind but don't have the added bulk of the guides in the insulation. I wear them from early august buck hunts all they way to october sheep hunts and they haven't disappointed me yet. To me, its a no bull shit pant that is nearly indestructible that does exactly what the name implies -- timberline stuff.
I am a timberline owner. For the price I am not ecstatic with these pants.
If it was somewhat wet and cold I think you'd be feeling it. I find they lack protection in the thigh area and in sleet/wet snow I have a feeling they'd suck.
If it was more desert like/open country conditions where you are brush past wet bush I'm sure the timberlines would be great. If you're in a mix of timber and 2nd growth these may suck. I know I was unimpressed with their water repelling abilities during some days this fall after rainfall when everything was wet.
I'd ask for opinions for weather as well as geography that they have been used in.
... You may have already but I can't re-review your post because I'm answer on my cell.
I used/tested them both out last year in CO during 3rd and 4th season. The guides were much more breathable, but didn't stop the wind as well as the timberlines. I love the hip vents, but found my lower body being colder while glassing in them. Keep in mind I had no baselayer on underneath. I believe with a baselayer they can be a very good mid to late season pant. DWR was great on the guides as well. The timberlines were heavier pants and warmer for me. They blocked wind better while glassing at the tops of ridges. I rarely overheated in them, but it did happen occasionally. During the mid to late season I'm typically at glassing spots during the colder mornings and evenings trying to spot game. Then I plan a stalk and go after them. The timberlines worked better for my application so I sold the guides. They are both solid pants.
Thanks for all the great replies. Made a hard decision even harder. My need for pants is actually wide and varied. I have the First Lite Corrugate Guides for early to mid and even possibly late if I get some good bases. I’m trying to find a pant for my late seasons which range from 40 with sideways rain in the thick brush of Western WA to 15 degrees in the snow and wind that the Eastern WA deserts often get.
In that situation I would use the Yukon pant with a baselayer underneath. I'm guessing that the Sitka similar pant would preform just as well. I just happen to have the Yukons.
I go back and forth with Sitka/Kuiu and find myself using a handful of both sets of gear. I wore the Timberlines and the Attacks 1st rifle season in CO this year. Temps (per my Garmin) mid 20 to mid teens at night and highs @40-45. I'm 6', 185 lbs, lean, with a fast metabolism and get cold fast. I was in the same boat earlier this year so I took both to end the confusion! I took the Attacks and the Timberlines. Both were great pants but big differences for me.
The Timberlines were warm and did a good job with wind, I sit on a pad when glassing (and typically throw on my rain pants so that I don't get cold) so I didn't "test" the seat being waterproof. I like the taper of the leg of the pant for gaitors, and the belt loops are beefy. These fit me really snug in the seat/hips and crotch but perfect everywhere else with the right pant rise too.
The Attacks were just easy, and wore like a pair of sweatpants. I absolutely loved the hip vents, non-zip front pockets, and they were more comfortable on horseback during the ride in to camp(9miles). I also noticed more stretch in the Attacks, which I really like. This could be because of the waterproof patches in the Timberlines (waterproof seat/knee). The belt loops aren't nearly as beefy and I could see them being an issue long term. No knee pads but thats never bothered me, if necessary I use my glass pad for my knee (cleaning meat).
Both dried quickly and DWR coated, and neither took on much odor either. Warmth wise they were very very similar to me with Sitka core light weight bottoms and SmartWool NTS 150 boxer briefs.
I'd also check out the Kuiu Talus pants. My Dad wore his for 6 days straight on this trip and they did great in these temps. He wore light weight base layers under them the entire time. He got hot one day on a lengthy hike, hip vents put a huge smile on his face. He said they blocked the wind really well also. He didn't wear his rain gear glassing, he didn't need the warmth.
I really don't think you could go wrong with either, both companies make great gear. I'll waffle back and forth but I really think Sitka needs to update the Timberlines (again) or add another pant to the big game line. Something that fits like the Apex (which I really like) with more warmth. I also wish they'd both start putting clips on the front of cuffs to hook to your boot and keep them down. Less logos would be nice too. If your backpacking I'd go with the lighter Attacks with heavy base layer. I like the guides but I'd buy the Talus if I wanted more warmth and roll with a heavier base layer (it'd be a lighter setup likely).