I have to chose between the two in the next month or so, I'm looking to take one up and stay pretty dedicated to it to help me get fit and so I can defend myself.

Right now I'm leaning towards Muay Thai (which is a martial art that uses knees, legs, hands and elbows) more because it looks more interesting and I think I could benefit from it more.

Boxing is good, too, though.

What one should I enter in your guys opinion?

Also, the fact that I have type 1 diabetes won't affect or put me at a disadvantage here, will it? (I'm not fat, pretty in shape, 5'9 140 pounds)

Muay Thai.

Muay thai.
Why?
Boxing only teaches punching to my knowledge.
Muay thai teaches elbows,punching,knees,kicking, and some more i think.
Also in Muay boran, i think you can headbutt.

I've did Muay Thai for a year and a half before, and i'm currently doing boxing. If you're looking to go into any fighting sports BESIDES boxing i'd reccomend Muay Thai, if you're looking to fight better in real life situations definetely go for boxing. Although, doing both at the same time(atleast for a while) would be pro.

i recommend boxing because its better for real life situations, but i would personally choose
ju juitsu or kick boxing

Muay Thai.

Muay Thai.
Those guys have really strong bones, and you might need a kick from time to time ;d

For real life fights choose boxing because if you do a flying knee and miss someone could punch you in the face, but for boxing you would learn how to punch stronger and faster and perform quick combos in case you wanted to beat the crap out of some guy. :3

muay thai
ive got two asian friends who do it and it's insane
and don't worry it definitely can beat the crap out of someone

Boxing is one of the best all round cardiovascular workouts there is. I doubt you will ever need to use either of these in a real life situation, so just choose the one you like the sound of most