Raikou. It's got an advantage over Suicune but no weakness to Entei.
Oh and he's the fastest, if I recall correctly.

Shedinja @ Life Orb
Bold
252 HP/252 Sp Def/4 Def
Sandstorm
Double-Edge
Leech Life
Rest
"Give a man a fish and you feed him for a day. Teach him how to fish and you feed him for a lifetime" - Lao Tzu