That is pretty much the whole problem with Magicka in Skyrim and why it does not synergize very well is the fact you cannot use it in conjunction with weapons. The game would be a lot better if you did not have to switch out weapons and magic in order to cast or swing...
well, you don't have to switch if you use a 1 handed weapon. That is part of the advantage a spellsword has- quickness.
On topic- since you cannot use spells without putting your big weapon away, conjuration is my vote. Nothing else is going to mesh very well
If you did restoration- then you have to stop attacking and go no offense to heal, so youll have to run away alot- I would rely on potions for healing in this case.
Destruction- you can't use it with your sword, so its a choice between destruction or 2 hander- 2 hander.
Illusion- It could work, if you frenzy or calm things before you begin, but if you have to pick 1 shool I would still go with conjuration.
Alteration- you really do not want to have an active defense (requiring repeated casting) for armor as a 2 hander, youll want armor. Course there are great magic defense perks in this tree, but they are pretty for up and require alot of investment.