For the main question it is much harder to answer as it purely depends on the strategy you would like to use in KB. (As you divorce once, you can't get this poor girl back)

Xeona is nice as demons are very strong units + she has 2 weapon slots (very handy)

Undead zombie girl / Bandit princess - she can be changed, has very balanced slots, and if you want go for undead army (as I do so often) she is the must (+ 1 speed + 1 initiative for undead)

Frog princess / frog : +3 INT (not such a big deal) or +100% attack to snakes (would it be + 1 init/speed to snakes - would be better)
Also I would not go for the +xxx% attack bonuses so much - is underpowered (once I maxed by cheating my INT to 4000 -> used berserk on shooters, - should be + 2000% to attack - my priests had 480 or so attack, did 380 dmg instead 100 -> is this really worth?)

Neoka is beutifull and has slots that can hold very useful items (regalia) but well, not to mention that many tactics praise the elven units, like dryads (I don't like elves - are wusses)

Mirabella - may be beutifull, but I really can't imagine she could be usefull later on in the game (still some players have good tactics with pirates... again these would be useless later in the game )

I liked dwarven units - canoneer, giant... so then the dwarven girl would be my choise - with dwarven units you can fight till the game end (have huge HP/ resistance)... would ressurection work on giants - I would never use undead units... sad is that dwarven units desperately need some other units to be mixed up with ... than you have a lot of planning in your way to re-think which units go as prior and which as secondary.

Your understanding of attack and defence bonuses is incomplete.

there is a 300% cap to increased damage for having a higher attack value then the targets defence..

+100% attack is very useful!

If you recruit ONE peasant, start a battle with someone, then run away (lose battle) is that considered as ONE battle? If yes, it would be trivial to 'complete' those 10 battles that way, right :) If you don't like your newborn, you would need just few minutes to 'pick' another one..;)

That would be quite clever strategy - still I believe that artefacts are better than the best child (even using next generation mod), not only as you can change them, but that they are actually really better.

who is the best wife for a warrior?

It is really depend on items you have, if you have 3x banner of true fate go for elfish princess :P.

There's no such thing as "best wife for a class" unless you plan on having babies. It's all about the items, although if you're trying to build up attack for some silly reason go for Xeona since she has 2 weapon slots apart from simply being awesome. :P

Dear Gamer Gatts,

Where can we recruit the following wives?
1) Xeona
2) Bandit princess
3) Dwarf girl
Thanks for your kind assistance

Danny

HI you can get married in following locations:
1) Xeona - Demonis, Castle where you get the key to Haas's Labyrinth
2) Bandit Princess (Rina) - In Greenwort, in the house of the Rotten Hake
3) Dwarf girl - Lower Hardar, lord's castle

Thank you Nike-it, I wouldn't do it better, I just can add a little note:
1) You have to beat Xeona in battle first
also you can hurry for her sooner than you get the key quest, even sooner than you resque the dwarven prince - if you would like to go for her ASAP, and are very skilled in running from neutrals :) Still you can't dodge the fight with Xeona herself
2) To get Rina (bandit/zombie girl) is possible if you succesfully finish the Zombie Miller quest - which comes very soon in the game and if you are skilled enough you can finish it at the nearly total beginning of the game
3) Her Father (sorry, don't remember his name) will give you old-school quest - SAVE MY DOUGHTER - this is tricky as well - you need to beat not few cyclops :)