Having played around with him a bit, here are my thoughts on each deities for the Goatperson:
Mystera - decent; her boons aren't very useful for the Goatperson, but she's an excellent piety farm and it's fairly easy to avoid her penalty with the constant swapping.
Taurog - decent, particularly as a piety farm; I haven't yet found myself grabbing his boons, but if I get a Taurog/Dracul combo you can bet resist stacking is on the menu. The penalty for using glyphs can be painful, though, given your dependence on fireball at low levels.
Earthmother - usually bad; unless IMAWAL randomly spawns on the map it's very difficult to earn piety with her, sharply reducing her utility. Aside from southern swamp or western jungle, avoiding punishment is trivial so she's seldom harmful.
Glowing Guardian - decent. Cleansing is very useful for the Goatperson, and protection plays to his strengths, but the other boons are impractical for various reasons so he's of limited value overall. Converting food is easy piety if you've got extras.
Jehora Jeheyu - nasty; poison and mana burn often force you to chug potions at uncontrollable intervals. I haven't had it happen yet (thankfully), but a late-game health or mana drain could be game-ending. His boons are very good, but his presence can really drain your potion reserves.
Binlor - decent; similar to Earthmother, if you don't have a form of wall-breaking he can be impossible to earn piety with. Fortunately there are more forms of wall-breaking than petrification, and if you can earn 35 piety from another deity you can always buy ENDISWAL directly from him. He otherwise works very well for the Goatperson.
Tikki Tooki - great, but risky; the punishment scheme of Tikki Tooki makes him dangerous to be on the board; with the food mechanic it's easy to get stuck in a no-win scenario early on. However, his piety farming abilities are great and his boon selection is exceptional, and the Goatperson's need to occasionally chew on popcorn early on means that with careful planning you can really get a lot of value whenever TT comes up in rotation.
Dracul - awesome; this is the best deity for the Goatperson, bar none. Oh sure, blood hunger will piss off two other members of the roster and blood tithe requires you to tread carefully (literally!) if you bounce to GG, but he is exceptionally well-suited to the religion-jumping. The ability to do things he hates (kill undead, quaff healing potions, use CYDSTEPP) when you're not worshiping him while garnering all the benefits of persistent Dracul worship are simply enormous. Since level-up heals aren't as meaningful for the Goatperson, Blood Curse is far less damaging than usual.