The Cosmo is nice in Leeds, but as has been suggested it can be a tad noisy on a weekend if you have a road side room due to it being in the vicinity of many bars. A number of colleagues have stayed there and have returned to stay there though as they've enjoyed the place. The restaurant is also one of the nicer hotel restaurants I've eaten in.
Other personal faves in Leeds I'd recommend are Quebecs, Residence, The Met and the Doubletree. The Rad Blu is also ok but again its in a very busy area of town that will remain busy into the early hours.
Also check out The New Ellington hotel. I didn't even know it existed but was rather impressed and that takes some doing when you're in hotels 3 out of 7 days a week