Inner vs. outer bar ends -- it's all user preference. A lot of variables contribute to your comfort with the bar ends. I have fairly wide shoulders, and I like to have my hands farther out on the bar rather than closer together. This is one reason I ride flat bars instead of drop bars -- drop bars just feel too narrow to me. This is also why I don't use inner bar ends -- I don't like the grip being that narrow -- I want more of a spread. If you're comfortable with a narrower grip, then the inner bar ends may be best for you. If you're comfortable with a wider grip, then the outer bar ends may be best for you.
Mechanical advantages of inner bar ends can include a more aerodynamic profile -- your body is narrower and probably lower as well. Mechanical disadvantages of inner bar ends can include less leverage on the handlebar/steering, since your hands are closer to it. You also can't utilize inner bar ends for climbing leverage, either. Outer bar ends are basically the inverse of this. Your body profile will be wider and possibly more upright as well, and less aerodynamic. But you have more steering leverage on the bars and more climbing leverage. Whether any of this has any impact on your ride will depend on where and how you ride, how fast you ride, your riding objectives, etc.
It may come down to simply trying both to see what you like. Or...if you don't like wider grips as much, and the only reason you don't ride drops is the low position, you can probably bet that you'll like inner bar ends. If one reason you don't like drops is the narrow profile, and you like the wider handlebar types, then you'll probably like outer bar ends.