hokiefyd 

One tire I'd suggest you consider is the Schwalbe Hurricane. It's available in 50-622, and I have a set in this size. They're available pretty inexpensively and are pretty supple for their cost (if smooth and comfortable is high on your list). Because they have a completely smooth/solid center line, they're pretty quiet on the road. They're also acceptably grippy off the road, due to their relatively low side lugs. If you run these with higher air pressure, these lugs won't really come into play and the tire will pretty much act like a large slick. If you run them lower on air, you get the benefit and the drawback of the lugs. The benefit is increased traction and stability on looser surfaces from these minimal "paddles" on the side. The drawback is a little bit of self-steer when leaned over on pavement, due to the lugs being pushed into the road.

I don't think they're all that resistant to puncture. They're fairly light for their size and they don't have any Kevlar or thick rubber underlayments. So take that into consideration.