I just got a Transpack XT Pro. It fits fine in aircraft overhead compartments (e.g., 737) as long as the center compartment is almost completely empty. You could fit a helmet in the center, but not if you want it to fit in the overhead. For day trips I'll be keeping all my gear in it to carry from the car to the lodge.
The MRV is I believe the largest Transpack (10% larger than mine), and appears to close a bit more securely making it better if you wanted to check it in with the airlines. For example, I believe you can tuck the backpack straps away. I considered it but found a local XT Pro on-sale for $40 instead.
BTW, you can fit quite a bit of stuff in your boots and in front of the boots in the boot compartments. I had full ski gear, including goggles, gloves, hat, ski socks, under layers, shell pants, and shell top in my bag with only the shell top in the center compartment, just to remain ready to ski should the airline lose checked baggage.
I'm quite impressed with the bag quality and layout. I don't think you could go wrong with a Transpack.