I just bought a new saddle for my bicycle, and I have to tell you all that having that slit or hole in the middle has made all the difference in comfort for me. It's relieved a lot of pressure on 'you know where.'
Anyway, I have to admit I was pretty clueless about buying replacement seats until I read a great article on what to look for. It addressed the pros and cons of material, shape, etc.
Another good resource on saddles is Finding the Perfect Bicycle Seat, by Joshua Cohen. It's an ebook available from RoadBikeRider.com. Cohen is a physical therapist who did an extensive study of the anatomical issues in cycle saddles and the claimed potential for injury, and presents his analysis and recommendations very clearly, with illustrations.