I would get both... eventually. They're pretty opposite of eachother sound-wise. The GAP is thick and colored, while the Auteur is bright yet full. Both have a nice fat bottom end.
I would use the GAP for snare (I don't have a GAP, personally, but I've used them a bit so I'm familiar with them), mainly because I usually am looking for a thick solid snare sound. When I record snare, I like a preamp that smooths out the transients a bit and gives the snare a bit more meat. The GAP is good for this. I also like how the GAP give the heavily distorted electric guitar some extra edge.
When I record drums, I usually have my Auteur on OH duty, because they pickup the cymbals so well! The Auteur is also my goto pre for vocals, acoustic instruments, and even electric guitar cabinets when I'm recording a bright chimey clean sound to bluesy crunch. I own six different kinds of outboard preamps and the Auteur is my most used one. It's clean and bright without sounding sterile, and always does a faithful job of capturing the sound I hear in the room. It's also fast and very responsive to transients. That's why I don't use it for snare.
I haven't tried the B12a, but for the applications you're describing, it should be a heavy contender as well, as API style pres are kinda made for these applications.