Dwarves are the fastest builders in the game, but due to their painfully slow speed, they generally won't make it to the build site until the peasants who finished it have all gone home.
They also only have decent combat stats (don't get me wrong, they're great in a fight, but it just doesn't balance out their speed), and are dreadfully greedy. While greed can be fine for encouraging them to smash something for you, it also means that they'll turn on you for a buck.
I've actually seen some dwarves go for something that not even a rogue would touch.
As for favorite temple, well... Krypta is great fun, and the priestesses can get downright scary at higher levels (shadow beasts and vampires can be charmed, if the map supports them). They also serve as a nice area defense, since the undead minions will patrol around the outside of the temple whenever the priestesses are resting.
The same goes for Fervus as well, and I've got a little soft spot in my heart for those crazy cultists... Shiny Bee will always be remembered for his bravery in times of... Utter safety.
Cultists are also pretty good at negating the irritation factor of sewer grates. They just charm the giant rats that pop out before they can nibble on anything (if they're close enough). They also serve the same defensive role as the priestesses by having their wild animal hordes sitting around the temple on off-time, but most of the animals they pick up are... Well, chaff. It gets better at a top-tier temple, when the cultists get a steady supply of hellbears for their disposal.
Rust spitters and wendigo, however, can really screw things up for whatever they're smashing. It's sort of the same deal as with Krypta, but applies to different maps/enemies.
For general use, however, Agrela's healers are absolutely my favorite. I can't tell you how amazingly useful it is to have these ladies running around and patching people up for you. They made it possible for a few city guards to fight off a troll while my other heroes were busy wandering around in circles. Plus, Agrela's healing and resurrection spells cost less than the chaotic versions.
Monks are also kinda cool. Vigilance is an absolutely awesome spell, and the monks are actually pretty good at beating stuff up. It's a shame that they can't buy upgrades, but that goes for most of the temple servants.
As for Lunord and Helia, I'd have to stick with Lunord. Helia's gals are really nice to have in a fight, but they're slow and they tend to be in the wrong place at the wrong time more often than not. Lunord's adepts, on the other hand, manage to be *everywhere* at the right time. They're not particularly great fighters, but they're excellent when it comes to those annoying minor enemies that pop up when you're not expecting them.
Krolm is cool, as in really cool... But I don't really think the barbarians justify missing out on all other temples. I don't know, I'll have to toy with them a bit more... They did, after all, get quite a bit more interesting with the expansion.