Speaking in extreme generalities, two cycles:
Lower cost
Lighter weight
Louder
Higher RPMs
Happier with "smaller" props
Less fuel efficient

Four cycle:
Higher cost
Heavier
Quieter
Lower RPMs
Happier with "larger" props
More fuel efficient

From what I've seen, two strokes work best when you need lighter weight and higher prop speeds. Four strokes do better where you need more "pull" and a little extra weight is not a problem. Of course these are generalities, because there are two strokes that love big props and generate huge amounts of pull .