well, i don't know about the best dorp in engine, but the picco .26 you mentioned is definitely the best drop in engine if you seal the backplate and a couple areas on the carburetor. it will make much more power than anything else that is a direct drop in. be prepared for wheelies and gearing up for more top speed.
They say a good mechanic only needs 2 tools - WD40 & Duct tape. If it moves, and its not supposed to, duct tape. If it doesn't move, and its supposed to, WD40.
Personally i found no better engine than the 3.3 traxxas, i only run traxxas, but others in my area have run others and none ever run better or run as reliably as my 3.3's
Work because i gotta, play because i wanna
People here hate Nitro, I love it. I start it, run it about 50 ft from me and it dies, I go after it. Perfect exercise
I had great luck with my 3.3's but at the moment I'm running a sirio .27 made for the revo and I love it. They are a bit pricey though. When this motor goes I'll be going back to the 3.3. I like them better than the os .18 i had in it too.