I started out life an an A mech but soon saw the light. I probably had one too many cases of GUE knee. Sorry!!!
It depends on whether you want to be green or not, 3 Commando Bde and 16 Air Assualt Brigade don't do A vehicles, apart from the BARRV at Chivenor. Unless of course you classify CVRT's as an A vehicle. Apologies to HCR.
My advice would be to go with either choice, nothing is ever set in concrete.You could always change your mind.