i wouldn't add guppies to a five gallon tank at all, they're pretty zippy swimmers and they do better with more room. better choices would be a betta and only a betta, or shrimp... or you could do some nano fish like microrasboras. guppies might suffer in that setup.
Aside from chasing the girls, guppies arent all that quick or active.. especially boys with fancy or big fins like deltas and swallows. White clouds put guppies to shame when it comes to being zippy fish..
Betta fish usually look depressed in anything less than a 5.5 or 10 breeder tank. They need stimulation from their environment.
Guppies are happy with little more than a couple buddies.