Psychic was unstoppable in the original broken games and although they have come back down to earth since that time I still always try to have at least one on my team. Crunch and other Dark moves tear them apart and are a pretty common move but I don't care.

Electric is also a great type which usually has high speed and only one weakness. Unfortunately, Earthquake is one of the most common powerful moves that almost any big pokemon can learn. But it is fairly obvious to see it coming so just switch to a flying type at that point and your opponent just wasted a turn.