Versatility - The stirling engine has great versatility
because it can be run on practically anything as it is an
external combustion engine.
Efficient - The stirling engine is theoretically
very efficient.
Quiet - The stirling's operation is very quiet; it just
hums along and is hardly noticeable.
Green - There has been a renewed interest in the
stirling as it is seen as a way to produce "green energy".
Great Hobby - Some low temperature stirling's can run
off the temperature of your hands.
Cons
Expensive - The stirling is considered to be slightly
more expensive then the currently used gas and diesel
engines.
Low power to weight ratio - The stirling is bigger and
bulkier than it's counterparts for the same power
output.
Not instantaneous - The stirling takes a little bit to
warm up and cannot easily provide instantaneous power they
are better at continuous power applications.
Summary
The stirling has been around for almost 200 years but
they are not in widespread use. In recent years a lot of
research has been done on these engines but it remains to be
seen whether or not these engines will overcome the hurdles
that they face and see widespread use. Currently they are
being used in just specialized cases and attempts are being
made to use them in electricity generation but it still
remains to be seen if the trend will catch on and continue
or whether they will just continue being the intriguing
object for the hobbyist.