Buggy

While not as powerful as other former Roger pirates, Buggy is a fairly capable fighter who was strong enough to survive all the battles with Whitebeard's crew and the extreme dangers of the Grand Line. His arrogance and greed usually gets the best of him, preventing him from fighting at his fullest.

While he was a considerable villain at the beginning of the series, he become a lesser threat as more powerful enemies showed up. Finally, in the Impel Down arc, the Baroque Works members commented how weak or how much of a coward Buggy actually is. However, he is still able to survive the ordeals that even the more powerful people can (albeit with their help). 

Buggy has very high endurance and resilience, since he survived an explosion from a redirected Muggy ball, with hardly any resulting injuries (though his Devil Fruit might have helped him somewhat), while a similar Muggy Ball severely injured Minotauros, one of the Demon Guards in Impel Down. He also possesses quite a great deal of physical strength, as he was able to lift and choke one of his underlings with just one hand, lifting a blugori easily and slamming it into the floor (although it got up again with minimal injuries) and managed to sustain the weight of both Luffy and Jinbe while floating with the upper part of his body (though this may be attributed to his Devil Fruit abilities).

One of the factors that assist Buggy in his exploits at least during the escape and the Battle of Marineford, would be his extraordinary luck. His uncanny ability to know the mood as well as his love of theatrics and saying lines at a precise moment strengthens the morale of his "crew" was immense. Most situations were resolved not due to Buggy's abilities but it all boils down to his immense luck. Due to the misconceptions of his selfish actions, ie: running away out of fear as something to do with the death of Whitebeard and their short term partnership, as well as catching Jinbe by accident but they believed that was his plan all along, many pirates become extremely loyal to him. Most of the times they were in tears from his "heroics."

If anything, Buggy can at least be seen as a formidable chemist. This was seen when he was able to create a cannon ball with enough power to destroy a town, as well as making it as small as a mothball but just as destructive.