OPS+ is kind of a subset of WAR (except WAR uses wOBA, wRC+ instead).
As to which one is better to use, it depends on the question. If you are only interested in offensive contribution, then I would not look at WAR. I would just look at OPS+ or wRC+. If you are interested in comparing the overall value of players at different positions, then WAR is better, because players who contribute more than just hitting need to get credit for that.