4 strokes generally make a lot of torque so they can turn a larger propeller. They also have a wider power band. A 2 stroke may have to run at very high RPM to make much power but a 4 stroke will make a lot of torque even at lower RPM's. Is one better than the other? Yes and no. It really depends on the application. Personally, I will run a 4 stroke if at all possible. I find that they idle better, have better throttle response and are easier to tune. When their propped right and sized right for the plane they have more than enough power. I also think 4 strokes sound way cooler than a 2 stroke. The biggest downside in my opinion is that 4 strokes cost more.

Also, don't put too much stock into the HP ratings used in engine advertisements. They are some benchmark number taken at some RPM that you will never reach in real life. Use them as just a loose guide.

Regardless of whether you go with 2 or 4 stroke, buy a quality engine and you'll be just fine.