The Commander is a grate Kayak, lots of room & very stable.
The Commander is so stable I am able to stand and fish at will. It tracks well and is fairly quick to paddle. The seat is comfortable but I rarely use it as I often paddle from the perch position. The one thing I would add if I designed it would be a small watertight compartment--I use a waterproof bag for my wallet, keys etc.
This yak is a lot like the Ultimate but it sits a little higher in the water and has better displacement. I also think it is more stable (the Ultimate is still very stable). All in all if u could only have one yak this would be my choice.
I wasn't a fan of the Ultimate's seating system that everyone else seems to rave about, but mostly since it didn't give me the back support I wanted for pedaling. I LOVE the dual height seating feature of the Commander. The "Captain's Perch" allows me to vary my position and paddling style on long outings and makes getting in and out as well as standing in the boat easier than any other boat I've tried, and I find the comfort of the main seat more than adequate. You sit farther forward in the Commander so it seems like you are in a smaller boat than the Ultimate, but the rear storage area is positively huge. My broken down paddle would not fit in that area of the Ultimate but lays flat with room to spare in the Commander.
One thing I dislike about the Commander is the floor. It is very irregular due to the keel running down the middle of the boat. I made floors for the front and back out of treated plywood and outdoor carpeting so my stuff (including my dogs) have a flat stable platform above any water that gets in the boat. The Commander has more freeboard than the Ultimate which is comforting but would typically make it harder to control in the wind, however due to the center keel molded into the boat it tracks straight and true even in high wind.
I tried on two occasions to re-enter my Ultimate 14.5 in deep water and was unsuccessful. I was able to re-enter the Commander relatively easy from deep water, which is an important safety feature. I think the difference may be related to the increased freeboard of the Commander. On another safety related note I found in both boats that the tunnel hull design makes bailing with a round quart sized or larger open top vessel much easier and faster than using a standard kayak bailing pump.
I like the fact that the Commander is pre-configured for a trolling motor as I plan on taking advantage of that in the future. It's also pre-plummed for the necessary steering cables and would be a relative breeze to do it yourself, unlike most other kayaks where adding a trolling motor to the back requires significant custom fabrication of mounts and cables, etc.
I really like the Commander 140 but I would probably have been happy with a standard Ultimate 14.5 as well. I had just gotten tired of all the useable space I lost with the pedal drive model. They are both high quality and quite similar but the Commander does have a few touches that I appreciate over the Ultimate. Your mileage may vary.