All these labels are excellent labels to collect, so good luck with the quest. Yeah there are a few duffers on Stax, and the odd duffer on Volt - but they are overall great labels, and I enjoyed collecting them. There are a few that are impossible to find - one by the Mad Lads on early Volt which is a surfing song and which I still don't have, and a couple of odd Stax things. And there's a couple of missing numbers too in labels like Gospel Truth, despite what Stak O Wax says.
Other major labels Ive collected in the past tended to be "classic" soul labels like Revilot, Ric Tic, Invictus / Hot Wax / MM, Loma, Minit, Glades / Alston, Abet, Wand (still need about 10 of these ) ,Goldwax, Philadelphia, Brunswick / Dakar, Buddah, Westbound etc. etc. And I can tell you that pretty most of them have a few duffers on - but despite that great fun to collect as you never know what you are going to turn up.