I'd say your question's like asking a person if taller or shorter people are more ticklish? Though yes, it can effect the placement of someone's nerves and how they react, it really doesn't answer the question.
A person's nerves being clustered around their feet and hands, those can be some areas that can be the best areas for high ticklishness. But as both appendages are used near constantly daily, it can also diminish the sensitization on either area as well. And just because someone has nerves, doesn't mean they're ticklish (sadly). It really depends on the individual person, their personal sensitivity, and whether they feel a greater movement of mass (larger muscles being moved when tickling a single area, moving more flesh) or more nerves in a smaller area (skinny people take up less mass, so the nerves have less distance to travel) is more ticklish for them.
I think a person's confidence has more to do with the ease of their ticklishness, so if they're able to feel more confident in themselves (skinny or muscular) it tends to make that person more easy to be vulnerable, and thus more ticklish as confidence allows their minds to be more at ease. Just my thoughts. Would love if someone could elaborate on how they think different, though!