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Well, I like to play both of them with a temple as well.
I will compare them by categories:
1) Melee -
The priest is about burning enemy creatures, while dazing and stunning them so they wouldn't damage the priest while the burns do their work. I've seen priests using that bow, but I've never seen a priest with that bow winning a game, as the lack of daze and stun chance just ruin that strategy. So priests should use the Staff of Asyra, which is an amazing weapon.
The paladin melee just go for tons of damage with his challenge ability. unlike the priest that go for a medium amount of damage but great conditions, the paladin deal a great amount of damage with medium conditions. That's a totally different strategy.
2) Training -
The priest have access to the crown of protection, that allow you a really nice 2 mana spell for the round you would like to save mana for a big creature in a later round (or round when you lack mana because you just summoned something big). Giving an armor +1 token is like giving a creature a leather piece, except it doesn't use spells from spellbook and doesn't take slots (and can't be dissolved). It also combine really well with angels.
The paladin have access to balista, a very good conjuration, especially when combined with a temple of light. The paladin also have in school spells like akiro's favor, and having at least 4 copies of this spell allows you to give a reroll to many of your creatures. An akiro's favor goes well with every creature that roll at least 5 dice (including knights of westlock, crusader griffons, Alandell, Ehren and some others). It's also really cheap to use on creatures other than your mage (only 3 mana). The champion's gauntlets are also a wonderful spell the paladin got access to.
3) Creature buffs-
The priest got the holy avenger ability, and it a very nice ability. The +5 life bonus combines well with the armor+1 tokens you can grant from the crown of protection. It also let you buff a creature greatly even when it didn't cost much to include him in your book. For example, let's start with a white cloack knight, a 2nd level spell. Now lets make him a holy avenger and give him an Armor+1 token, and we get a creature with 13 life, 2 armor, an attack of 4 dice that can be increased to 6 piercing +1 against enemies that attacked this round, and he is even immune to attack spells (for just 14 mana and 2 spellbook points).
The paladin have some awesome auras that benefit the creatures in his zone. The problem is that you need good positioning to keep them in the same zone as your paladin, but things like melee+1 piercing+2 to every creature in your zone is pretty awesome.
4) General abilities-
The priest have its creature do defend itself, while the paladin is there to defend his own creatures.
The priest have a holy avenger that get a bonus against an enemy that attack the mage, and the priest also daze his enemies so they couldn't attack him back. The paladin have an aura that allow him to take damage instead of his creatures, and if his challenged enemy attack a target that isn't the paladin then the paladin gain valor from it while the paladin allow his challenged enemy to get the same rerolls he get while attacking the paladin and not his creatures.
Overall. these are two very different melee holy mages, and I really like both of them
