Well, not many good TF players will leave HDD alone without support here are some common combos and their counters for armies with a max of 20 units
Combo 1 (TF): 8 HDD, 4 AA mobiles, 6 MD, 2 AM.
Counter 1a (Gung): 3 famba shield gens, 14 MD, 3 jedi nights (turn three of the HDD, keeping your masters under your shield).
Counter 1b (Reb): 20 air speeders. Take out AA, rest is dead.
Counter 1c (Empire): 8 DarkStorm, 3 AM, 9 MD.
Counter 1d (naboo): boy, can't think of a cheap counter. Naboo units are so expensive.
Counter 1e (Wookies): 10 MD, 5 artil, 5 berserkers.
Well, that's usually what I use :0