Both are great engines and they still make the 250. The 250 is a bit more complex than the 240, but both can be intimidating to work on, as well as you need to find a certified Mercury repair shop and not a Sea-Doo dealer to service them.
I would look more at the hours that the engines have on them and how the boats have been maintained, rather than worry about whether it has the 240 or 250.
Aaron:cheers: