The general rule of thumb with helis (both full scale and models) is: The bigger it is, the easier (more stable) it is to fly...

If you live in a windy area, and want maximum stability, you should get as big a heli as your pocketbook will allow. For electric, get the T-REX 600... If you don't mind dealing with glow, then get a .50 or larger heli. The Raptor .50 is a very popular choice for beginners...