I really like both.Why would you chose a arm in over a high elbow? Control?
Hmmm. I mean it's not news to say the high elbow is a faster and stronger finish but the arm-in is more control.
I used the high elbow more than basically any other technique is grappling from 2010-2012. I think now I use the arm-in more just because I've improved my ability to finish it and I like the extra control and transition options to the back, the brabo, the anaconda, etc. And I even like going to the high elbow from the arm-in. So usually I try to get the arm-in first and use it as a launch pad.
One time I do try to get the high elbow straight away is from seated/butterfly guard. People are good now as throwing their shoulder into you and trying to pass as soon as you get any sort of guillotine on your butt. For me, throwing the elbow high helps stop their pass and you can even finish it if they complete the pass. For the arm-in from seated guard if they start the pass you've got to be ready to either shrimp, let go fast, or switch to a brabo choke as they are passing you.
From the top it's almost always arm-in guillotine control first. Then I'll either finish or switch to high elbow, brabo, or I'll pass, or back-step to 411, etc. I love the arm-in guillotine control from the top in almost any position.