2 v. 4 cycle
By "moveable transom" I assume you mean that the boat has an outboard mounting bracket on the transom. Both the 2 and 4 cycle outboards have pros and cons, but its probably safe to say that the market is shifting over to 4 strokes. I bought a new two stroke a couple of years ago (Nissan 8 hp long shaft elec start) and it has been great. 2's are still lighter and less expensive than 4's, especially if you want the long shaft electric start models, although the gap is closing rapidly. If you want a 4 strok, be careful; 4's not only weigh more per hp, they also generate a lot more torque. They need mounting brackets specifically designed to handle their weight and power. Check the bracket on your boat carefully before you buy a 4 stroke to ensure it is rated to handle a four. Unfortunately if it isn't, you may need to fabricate a custom spacer block to accomodate the larger, beefier bracket so that it can be mounted on the transom.