The Import units continue to be popular with Honda leading the way with very reliable units. Most of these units run at 3600 rpm to maintain 60 hertz. Keep in mind these high speed units were not designed for prime power, but are great for backup power and construction work. Some of these models have features like auto idlers that slow the unit down when no power demand is on and low oil shutdown, in case you forget to check the oil. A genset is a generator with an engine attached to it.
Some generators are available as separate units that require a drive source.
A genset is only as good as its weakest part, so look at the total package when you buy. Most small gensets are rotating field generators. These units are self exciting and rely on residual magnetism in the rotor core to get things started. This DC voltage supplies the field which rotates in the center of the unit and induces voltage into the stator windings, located in the generator case. Here in the USA it is usually 120 or 240 volts, primarily single phase in small units.