The 240hp is the old school EFI two stroke where as the 200 optimax is the newer direct injection offering from Mercury. The 200 will yield significantly better fuel economy and make virtually zero smoke. The tough question is about the reduced power of the 200. If wakeboarding and watersports are on your agenda it makes it a tough call.
Which ever you choose be certain to have the engine checked over by a certified mercury technician. Should you get stuck with a rotten apple your used boat is going to become an expensive proposition.
Craig