If you desire best power/weight ratio in your models as a gasser, I'd recommend looking into EVO/MVVS 26cc engines. Light, powerful, same size and similar weight as a 160 sized glow engine without the drawbacks. Also they exceed expectations with a tuned pipe.. The only drawback is their price.

For scale, sport flight, the heavy, a little pricy, but dead-reliable Zenoah engines are very good choices..

Chinese CRRC (cermark sells them) 26cc is also a very good engine for its price. (Its also sold in Hobbycity)