Did a bit of learning on both and have used a bit of both since...grass tends to flatter my landings as its usually a bit softer than hard, but you do have to be very circumspect about potential prop-strikes in tricycle aircraft , its v. important to keep the weight off the nosewheel as much as possible. Take offs, conversely, can be a bit of a random affair as small bumps and lumps can have you skipping down the runway before the aircraft is really ready to be airborne.
Grass can also be surprisingly draggy for take off and slippery for landing, take a good look at the relevant Safety Sense leaflet. I also seem to recall the Thom manuals cover this area pretty well, in particular the performance factors you need to apply.
