I mostly agree with Lujo on Mystera and Taurog. The wizard is already so good at spellcasting that Mystera does little to help him further, and there aren't many dedicated warrior classes in this game so Taurog has relatively few followers that fit his narrow niche.
As for god preps penalties (from worst to best):
Dracul: I find that since having him by the entrance isn't a huge deal, and his penalty can potentially be a game-ender the boss ends up bloodless, so I just never prep him. What's the point of an anti-scumming mechanism when it can screw you over randomly? I go with four altars instead.
Tikki Tooki: pretty steep penalty, but this guy is very nice if found early. Again, I rarely prep him because that penalty is so steep but unlike Dracul there's a strong case to be made for his sheer power.
GG/Mystera: these guys are functional, and seeing as they benefit enormously from immediate worship their penalty is (for all practical purposes) self-cancelling. That said, they will never be quite as powerful as they would have been if you'd located them early naturally.
Jehora Jeheyu: this guy's penalty is annoying as heck, but it can at least be mitigated by a compression scroll. Furthermore, this is a deity whose general downsides can be more easily controlled if you bring the right preps, so ironically predictability makes Jehora run much more smoothly. More than any other deity, he benefits from early worship, so all things considered he still makes a sensible choice. I still loathe giving up inventory space, though.
Binlor: superb pick for a variety of reasons, though the reduced number of wall tiles means converting out is mandated earlier than normal. Overall this is a fair tradeoff, and the only class I'd hesitate to take it with would be Paladin (who cannot convert out and is stuck with the reduced wall tile total).
Taurog: this deity is weird in this respect. I virtually never want to see him appear randomly since he just doesn't work with the majority of build/classes, but when he does work he's so good that prepping him is a no-brainer. The penalty is basically a non-issue; cowardly is generally a neutral trait that is helpful in some circumstances but harmful in others.
Earthmother: this is the only deity where the prep penalty is actually a bonus! One of the problems Earthmother worshipers often have is creating enough plants to fuel clearance. This "penalty" loosens that constraint enormously.