I also have two "design series" going in stunt at least. I also have works in progress in scale, carrier, speed, TR and combat...
I'm finally getting somewhere with my long drawn 'go for broke' moulded stunter, but the wind design question has split off another path to follow, so the technical aspects involved there has spurred my interest. I have wanted to build a Hooptee for Classic for a while now, but seeing the Stunt Machine pics on SSW has inspired me to look for that plan.
I guess it comes down to Fire in the Belly, as Dave said. Whichever one grabs my enthuiasm gets the attention. I think my schedule this year calls for 11 new models before our Nats in December.