I say get whatever you can live with. If this is your first cab and you are playing mostly newer (90’s) games, I say go with a TV. No use paying $300 extra if you just want to play the games and have fun. Much cheaper, and usually easier to set up. May be a little tricky to mount in a cab, but it can be done easily.
If you want authentic arcade resolution, get a CGA arcade monitor. You will probably spend lots of time experimenting with proper resolutions and settings for each game.
Personally, I have a 27" TV in my first MAME cab and I am very happy with it.