Bryce Canyon NP has easy, moderate, and strenuous hikes. There's a rim trail that is probably the easiest of the bunch, with the Peekaboo Loop, Navajo Loop, and Queen's Garden all in the up and down category, and they all intersect. The Fairyland Loop is long.
The Welcome Center Rangers have all the info on which are which as far as degree of difficulty. It's a good idea to touch base with them before heading out.
If you don't mind some serious vertical trails, I'd take BCNP over any of the others. I guess I'd say Bryce has the best variety of hike options for every skill level. Last time we were there they were working on adding asphalt trails from the town into the NP, presumably for walking/cycling/roller blading??? They raised the camping fees to pay for it.
I'm not a great hiker, I just like the hoodoos.