Do you have any friends that will be bringing their air tools to your shop? If yes ask them what style they have. M and A are the most common around here. I have the M style.
When I started out, I went with "T" only because it was my first initial and I could remember it that way when I went to pick them up when I needed some more...
Started with "M". Found they were hard to connect . You have to pull back on the connector to install. Went to "V" Liked them better as you push the connector in. The "G" connector uses M,and A fittings. I was using M so I was OK. Naw the "M" leaked. If you play with it the leak will stop. Tried reconnecting. Still hit or miss. So I tried "A", worked great, no leaks.