You weren't specific about how much lawn you have or your age / physical condition. Also, you gave no indication of the slope of your lot. Level? Rock outcropping? Hillside?
Personally, I have never owned a rider or tractor. Too big too expensive, and I like the excercise. In fact, my current mower is the first I ever bought with propulsion.
My lots have always been between 0.5 and 1.0 acres. Subtract maybe a 1/4 of that for house, driveway, sidewalks, and landscaping and a 22" walk behind mower will cut a lawn like this in a couple of hours and it won't take up a lot of garage space.
5HP is enough but they seem to increase power every year and you can find a 6.5HP craftsman for $300-$400 that is self propelled. All of the small engine companies make decent small engines, Briggs, Koehler, & Honda. They will all last at least 5 years, probably 10 if well cared for. A Sears store is generally easy to find, they back it up with a service dept, and they're a pretty good value.
One other note, if your lot is sloped badly, a rider or tractor can be dangerous (tipping). Be careful when traversing a slope with a narrow wheebase / high center of gravity (you) vehicle.