Should I use gloves or track mitts?
Fit: Track mitts have a very different fit around the palm because the cut does not have to take care of finger length, especially the change of finger length when bending the fingers.You will notice mitts fit snug around the circumference of the palm. This allows to use different materials, which do a better job of protecting the palm from chafing or road rash. Gloves need room at the back of the palm to accommodate the pull of material around the knuckles of bent fingers. 


In my opinion, track mitts have a much better feel on the palm, even with a comparatively stiffer material.


Protection: Track mitts only offer protection from controlled crashes where you land on your palms. Mountain bike gloves are made to protect the outside of the hand, particularly the knuckles. The gain in protection is well worth the downsides in fit and chafe protection. Additionally, rides where you need protection of your knuckles are not as long usually. (Mmmhhhh 100km downhill!). Btw, historically, track mitts started as breaking gloves. 100 years ago, they used to brake with the leather palm. 


I do have winter gloves that are made specifically for bicycling, and they do a good job of warming the hand. But the more elastic material on the palm shifts all over the place on long ride, despite the seemingly snug fit of the gloves. 

Btw, I once had some particularly comfortable track mitts that completely failed in the protection department, on a crash the palm material just peeled away from the palm. Go leather, I say.