
[pet]Young Venomfang[/pet], in a way, reminds me of [pet]Nether Ray Fry[/pet], as in, having a wide variety of damage types -notably including the fairly rare
Undead type- but nothing really remarkable besides that - fragile, and without any "big" moves.
Its only truly "unique" move is [ability]Toxic Skin[/ability], and if I were to choose that one, I'd probably aim for
H/P breed. Speed is great to make this move proactive rather than reactive, but considering you'll likely have speed advantage at the start of the match (due to Flying bonus) it makes sense to aim for a bit more endurance. Still, not a huge advantage or disadvantage over
P/S, which is also a good all-rounder, so the only consensus is that P/B is the worst.

As for [pet]Cavern Moccasin[/pet]... Considering the trademark of this pet is [ability]Squeeze[/ability], being forced into Speed breed is overkill. Considering you sacrifice [ability]Burrow[/ability] in the process, and that you could even fall back to [ability]Hiss[/ability], makes Speed all the more pointless. Why can't there be a H/H or H/P breed for it?
So in terms of breed, S/S is very standard for snakes in general, and for this one in particular, a single [ability]Squeeze[/ability] is enough to gain Speed advantage over even fliers with any breed; so S/S is out and S/B is an instant discard. That leaves
H/S and P/S. I'd lean towards
P/S, solely because it'd beat the
H/S if they were to "duel", as the massive frontloaded damage totally removes the Health advantage, but like with [pet]Young Venomfang[/pet], the difference is so minimal that you can stick with whatever.