I'm currently riding Schwalbe Marathon Plus tires in 32c on my Big Block and I've used 28c Panaracer Ribmo tires on my other bike, both bikes are fixed gear and I have no issues with those tires. The 32c Marathon is indeed a little bit slower then the 25c gatorhardshell I used to have in there, but the added confort on rough roads makes up for it. The puncture protection on both tires is excelent, I had the ribmo in the foldable version so it was very easy to mount on the rim, the Schwable Marathon has a wire bead and can be quite difficult to mount the first time, but you don't need to remove it until its time for new tire since you'll most likely never get a flat.

If you're looking for a comfortable ride get a Marathon Plus in the largest size you can possibly fit and you wont regret it. You can always keep a second pair of skinnier faster tires for road rides.