Mid-Length is the best compromise in my opinion. Even with a 16" barrel you get a longer sight radius and a slightly better gas system. I really see no advantage to the carbines with the short handguards.
I could not agree more. I had one carbine, and I liked it well enough, but I sold it and have a 16" with midlength system. But if you're going to have a 16" barrel, go middy for the gas system and longer sight radius. Indoors-midlength outdoors-rifle!