Which is more powerful?

[Hento]

After playing for a while, I've come to the conclusion that playing as a mage is very frustrating because you are always drained and never have enough mana to fulfill your spell capacity.

[Kathos]

Which dragon have you started with? Starting with mana accelerator may help as you can place the orb wherever you want instead of it being random like in KBTL. Also, are you working towards transmute as soon as possible? Inquisitors can easily supply you with the rage you need to fund mana accelerator until you can pick up transmute, and then possibly work towards the rage income in the warrior skills. Picking up some tanky units can help too, such as paladins if they are available early albeit rare. If you can manage to pick up the Bolo chart you can sneak by everything starting from the Drakkar ship into the drone guard caverns as well as kite away the hero to pick up the amulet (make sure nothing follows you within aggro range of entering the cave or getting out is impossible), handing that in to the temple on Debir (near the stonehenges, use the amulet for +50 leadership before handing it in) will give you paladin's at the temple near the castle. Also I believe there are cyclops in the viking camp, just up the hill from the guy with the quest for his wife.
It seems like the mage has to play more like a rogue and sneak around kiting guards away and stealing everything you can from at least the first few islands before you can really start fighting much of the bigger armies. Pick up as much + intellect as you can so you're getting more bang for your buck as well, there is a lot available early in the paladin and mage skills.

[Zechnophobe]

Using just archers only works on lower difficulties I find. Otherwise you end up just not being able to do enough damage against large foes. My current Hard warrior uses Black and Red Dragons, Inquisitors and Paladins, and Demonologists. Dragons tank very well, and do large amounts of area damage. Paladins and Demonologists are your tank units that you pit against 'omg' stacks, (Demonologists by summoning, paladins by being paladins) and inquisitors are my only real archer.

I have both max blood lust, and max voice of the dragon, so yes it is fairly far into the game. This combination of items/skills/troops has a lot of tactical options available to it.

[Hento]

Are there any items that in some way enhance mechanical units?

[arcainic]

I recall an item that -20% leadership cost for drones

I think the best damage are actually from bowman with telescope (+100% atk) item, and +damage items (the poisoned dagger). But i was playing mage as main (for the double cast), it was sux0r even with the poisoned dagger and telescope.

Something's serially wrong when dragon dive is outputting more damage than all my doublecast + creature damage combined.