I am assuming your taking about a 2006 challenger 180? challenger 1800's were two stroke, the 180's are four stroke, resale value is better with a four stroke I think and better on fuel with no smoke. but you are also comparing a 20ft to a 18ft boat so depends on what you want. depending on what type of water you are on. The bow is pretty low on the challenger 180's which is ok if you are on smaller inland lakes. The utopia will porpoise more because of a flatter bottom, installing trim tabs can help but added expense again. the merc engine in the utopia are typically fairly reliable but can be expensive to repair if you did have an issue, the engine in the challenger is very relaible as long as the supercharger maintenance has been done.