The Fun has plastic bushings, a foam canopy, steel main shaft and steel tail shaft.
The ECO has bearings, a lighter plastic canopy (that stays on better) and CF shafts.
I think the fun comes with a 295 motor and the newer ECOs come with the 310 tuning motor. There is barely any difference between these motors.
Getting a Fun kit with a bearing upgrade gives you most of the advantages of the ECO with less cost.
Get an aluminum hub upgrade. It has screws to hold on the tiny bearings. The plastic stock hub has been known to let the bearings go when the rotor detaches in a crash.
For more info on the Piccolo, check [link=http://www.pgoelz.com/piccolo_faq.html]Paul's site.[/link]