Display size+orientation?

[Max Power]

I am in the planning stages of my MAME cabinet and would like some advice, please!

First, I am going to use an old Asteroids cabinet.  (Let me explain why I am converting a classic cab, lest I get flamed: This was an Asteroids that had been converted at some point to a Star Trek.  The Asteroids artwork is gone, the control panel is hacked up to accomodate the ST controls, and many original items have been removed.  I am not trashing the ST stuff because I need spare parts for my dedicated ST upright.  I bought it for that purpose, but thought I could make good use of the gutted, hacked-up Asteroids cab for a MAME cab.  If anyone has a good argument against that, I'm all ears, but there seem to be a lot of Asteroids out there, and I don't have the skills to do a proper restoration anyway.)  It is pretty narrow compared to typical MAME cabs -- width inside is 24".

I have already decided, due to costs, to use a TV as a monitor.  What does the kind forum recommend, in terms of TV size and orientation?  I could fit a 24" (diagonal) TV (decased) horizontally, or a 27" TV vertically.  I would be playing both types, being a fan of so many classic games (Defender - horizontal, Centipede - vertical).  Or maybe there is another option I'm missing...