User blog comment:Blackendedsoul/Devil Fruit Limits and Physical Ability/@comment-4605926-20120122182444

Well, I assume Zoans are out of this discussion then, since they don't have this kind of abilities and that their transformations are simply gained by the fruit itself which gives the user the animal's powers. As far as I remember Logia Fruit users can generate near limitless amounts of their element regardless of their training with it. As for the Paramecia types of Devil Fruits I bet Luffy can stretch further now (I bet that simply stretching extremely far wouldn't be very beneficial though) just like Robin can create more body parts (she mentioned it on their way to Fishman Island in the Anime, perhaps in the Manga aswell but I wasn't reading the Manga at the time). Anyways, I think the question should be more like - how well they use their techniques and how lethal they can make them. Well, I haven't actually eaten a Devil Fruit in my life so I can't really tell for sure but it seems like one has to be quite creative like we've seen with Kaku and Kalifa during the CP9 Arc. After you've passed the creativity stage you obviously have to train your Devil Fruit powers in order to get the most out of them. Conclusion:

Logia - Can produce limitless amounts of his/her element, given with the fruit. Gotta be creative though just like Kaku and Kalifa to find the ability first.

Paramecia - Can extend its limits by training just like Robin did.

Zoan - Gotta be creative in order to find the way to transform (partially or fully), power given by the Devil Fruit itself, ummm, perhaps can be enhanced through physical strength.

Hope I showed here valid discussions