lasauge 

I've used modern Shimano and Sunrace freewheels and as others have said they work well, are cheap, and shift better than old freewheels because of the ramps and shaped teeth. I have had problems with modern freewheels, but the common factor in every case was that I only had issues after the freewheels were used for an extended period of time for winter commuting duty - I'm not sure whether the issue is with the factory grease or something in the design, but whatever it is doesn't seem to matter unless you plan to do a lot of riding in sub-freezing conditions through snow and ice.