For me, it's G. Carapo. I have yet to see one at any of my lfs. N. Notopterus comes in once in awhile for me. As for A. Camposdapaz...not sure if that's really a new species (tried looking it up)...I know that they've made a couple of morphs of A. Albifrons and the Blushing BGK is just one of those morphs. They just became available at my lfs last year, so I'm not sure if they're going to be a seasonal thing or once in awhile thing.
When it comes down to it...this is what's rare for me (in order of rareness):
1. Gymnotus Carapo
2. Apteronotus Camposdapaz
3. Eigenmannia Virescens
4. Apteronotus Leptorhynchus
5. Notopterus Notopterus
6. Chitala Ornata Gold (with no spots)
7. Xenomystus Nigri