This is where Kega Fusion shines. Not only does it emulate the Genesis, Sega's most popular console in the U.S., it also emulates the following Sega consoles, according to the website: "Sega SG1000, SC3000, Master System, Game Gear, Genesis/Megadrive, SVP, Pico, SegaCD/MegaCD and 32X." That means you have all your Sega emulators in one piece of glorious freeware. No more switching between two emu's to play different games.
Not only does Kega Fusion emulate almost every Sega system for use on the Mac, it also has a handful of useful features. Each game gets 10 save states that are easily chosen and used. When you install it the proper BIOS are included, which means you don't have to search the internet to find them (very handy!). Also, it has full USB controller support. Oh, and it emulates pretty fast too. In fact, I've never had a problem with a game not loading or freezing on me. It works perfectly. What more could one ask for in a Sega emulator for the Mac? Nothing.