For a small lawn a walk behind will be as fast as any rider. I would look at a good quality 21-inch from companies such as Honda, Toro, Snapper, or Ariens. It depends what dealers carry in your area and which model fits you specific needs. You should also decide whether you plan to discharge, mulch, or bag. Some of the mowers will perform better in one area than in another. For example the more expensive Honda's rear discharge. I have always found rear discharge to be a bit of a pain to work with as a lot of the clippings end up on you. They work well in both mulch and bagging mode.
Scag Tiger Cat 48-inch deck, Kawasaki motor
Lawnboy 10227 2T push mower
Stihl BG86 handheld blower
Stihl BR550 backpack blower
Stihl KM110R kombi system with lots of attachments
Stihl HS45 hedge trimmer 24-inch blades
Echo SRM210 trimmer