ORIGINAL: Motions
Usually the rule of thumb is, the biggest the heli the more stable it is. If you get a shogun or swift they have more mass and are heavier so they tend to be more stable. If you have a Blade CP or Trex then they are much lighter and very squirrely.
Er, bad comparison. The century swift is closer to a .30 size nitro and is much bigger than the shogun. Shogun and t-rex are about the same size, blade cp is smaller than both.