So far, out of the big three combat-worthy magic mods I'm playing with, I've determined that...
* Thaumcraft is very easy to get into at very early game and all the wand focuses make for very damaging and durable weapons.
* Blood Magic can't even get started until you have a good pile of diamonds and emeralds and seems utterly useless until you work your way towards Bound Armor and Bound Tools at which point you're a demigod as long as you make regular sacrifices.
* Ars Magica can't really start until you find enough specific ores to build an occulus and then build a giant megastructure to make yoru first spell, so it's not very early-game friendly, in my opinion. Mage armor is extremely potent, but the attack spells can't punch their way out of a paper bag and burn through your mana way too quickly for the amount of power.
Just got into a throwdown with my Ars Mage buddy and wiped the floor with him using my Blood Magic, although I exhausted all my essence and was down to a single heart when I finally killed him.