Shockley
Maester
I could argue Tyr since he was the god of war, but many of the Aesir and Vanir were formidable warriors.
I hear the 'Tyr is a god of war' thing all the time, but I've never come across any actual sources that point to him having that role. He was, fundamentally, a god of government (specifically over the administrative bodies like the Althing, though this is a role he shares with Forsetti) and justice, though he seemed to have some role in determining whether one received their fair share of recognition and glory.
The only idea, in my mind, that actually associates Tyr with war is the idea of the Romans that he was the God Mars. That said, I don't think that comes from him having the portfolio of war. Mars was not (as Ares was) a 'stupid' god - he was intelligent, shrewd, and above all else, was seen as the father of the Roman people and the preserver of internal peace (through readiness for war). In that sense, he does have a lot of similarities with Tyr.
As to who the proper war god is, that is a complex question. Odin certainly had some authority over matters of war, as did Freyr and Freyja (all of the Vanir, to some extent, seem to have some special relationship with war). Personal combat, as distinct from war, would have encouraged one to follow a god like Thor or Magni. If one was pursuing a war of vengeance or a personal vendetta, someone like Vidar or Vali would have been appealing. Battles on the sea would have brought one to Aegir or Njord (more likely Aegir, as he was the more violent).