Kickboxing was infact the original MMA back in the day, which styles better? TKD? MT? Savat? Kickboxing was the answer. Everyone got together and fought it out, some stuck together, some imitated each others styles, and eventually they turned into 'kickboxers' like BJJ guys turn into 'MMA' fighters today. I wasn't aware of this until recently so I thought it would help you understand kickboxing a little better.
I have to say though I agree with every single post saying that it solely depends on the kickboxing instructor, because it does. Maybe visit both gyms, try out both, chat to the students there, do they compete? What rules? Do they cross train? Have they 'DONE' kickboxing if they train Muay Thai or vice versa. It's also good to check what 'style' of kickboxing they practice then go home and google it, have a read and then assess the situation from there.
Good luck buddy
'Dance' 
I have to say though I agree with every single post saying that it solely depends on the kickboxing instructor, because it does. Maybe visit both gyms, try out both, chat to the students there, do they compete? What rules? Do they cross train? Have they 'DONE' kickboxing if they train Muay Thai or vice versa. It's also good to check what 'style' of kickboxing they practice then go home and google it, have a read and then assess the situation from there.
Good luck buddy