They do differ slightly in the way they preform on the battle field. Gengar is more hit and run style,Creating massive damage in one or two turns then kicking the bucket. While Joelton is slightly more enduring style. It hits hard, fast and often, KO-ing opposition that way instead. Looking upon movepools, although Gengar can learn more moves its faced with a fair few weakness,while Joelton has only one. This means that Joelton can use moves more freely rather than covering for weakness. So...on the whole Joelton would be better. Although Gengar is still pretty epic.