I went magic combat. As a Mage or Battlemage, I favour a strong burst of magic from my hand or staff. If i run out of MP, or the enemy is resistant, that's when I pull out my sword (usually enchanted) to lay into the enemy. I also use Soul Trap a lot.

Have you ever tried a Nightblade?

Honestly I almost always play a carefully customised blend of all three. I suppose I primarily stealth it up as I like ghosting through places acting/investigating/silencing through force as I see fit but it's a careful balance for me and it all complements each other/how I'm choosing to roleplay that character.

Pure magic has always been the most fun for me. I recently mastered the illusion skill, and it has really opened up a whole new style of play.
However, when I'm making a character to be powerful, I always go for a hybrid between sword combat and magic. My shield and soul trap spells coupled with an enchanted sword haven't let me down yet.
Combat alone is probably the weakest style in my opinion. I'm not a big mod user, but Deadly Reflexes has certainly rectified that problem. Something similar would be a welcomed addition in future games.