Realistically, semi-auto, if I need 3 or more 30 rounders in any one firefight I am probably not coming out in good shape.
I have 9 30's for my AR.
Almost all my ammo is on 10 round stripper clips for easier reloading convenience.
I can't carry more than 7 or 8 in my vest anyway.
Good to have spares though, just in case so I need to get some more.
I have 5 15's for my 9 mm.