As far as single handing goes
there should be NO difference. The issue with SH is to have the lines led aft, an easy reefing system and an autopilot, unless you are so good at sail trim that you can use the wheel brake (only tightened halfway). If there's a tiller, it's even better because you can use John Letchers self steering with lines as an autopilot. If you don't want to go back to the dark ages, then by all means buy an autopilot, which, BTW, will teach you good sail trim.

Either boat should do just fine. In addition to all the get-a-good-survey suggestions you may hear, the one thing I would look for in an older C30 is an upgraded traveler. If it has the old curved track and/or one with only a 3:1 purchase, it will be almost impossible to adjust. It's relatively in expensive to replace with a new Garhauer traveler system.Roller furling would be nice, but not absolutely necessary, since you can install a jib downhaul line, heave to starting on port tack, and then bring the jib down on deck all nicely self-folded.I singlehanded our C25 for 11 years and our current C34 for the past eight.I find that with our boat, and the cockpit layout of a C30, that especially with an autopilot you will find yourself in front of the wheel more often than not once you've set a course and are sailing.Install the autopilot control head where you can reach it from both sides of the wheel (front and back) or else you'll become a slave to being behind the wheel. You'll find that location limiting and boring after a while, since it's further from the center of fore and aft movement of the boat (which is generally around the entry to the companionway).Go for it, you'll love it.