Depends on the size of the engine your starting with. My first engine was a 12 lb PST and I had it in the AV8R for three years. That engine was upgraded to 14 lbs and has been in both a Reaction 54 (built up) and a Shock Jet for the last 4-5 years. During that same time I bought the PST 1300R at 28 lbs and I put it in a Boomerang XL in 2005. Just last Aug, I swapped out the 1300R and put in the Jet Central Rhino in my Big Boomer which is still going strong. The Rhino makes the Boomer a whole new jet to fly. There is also the Reaction ARF, Facet, Turbinator, BobCat, Elan, Boomerang Intro, Sprint, Torus to name a few. I personally enjoy my Boomer now, especially with the big block for push.
Just choose the size of engine you want, pick an appropriate airframe and go fly. They all fly well, except for the Shock Jet due to it's spin, so you really can't go wrong.

Roy