Both are actually pretty solid games in my opinion. Black Ops 3 actually made the advanced move meant system smooth and fun to use mixed with the addicting multiplayer of Call of Duty made for a good time. Halo 5 probably has the best multiplayer in the series and Warzone is phenomenal. The only downsides to both are the Campaigns. Neither game really has a good story at all. Personally though, I feel like Halo 5 is the better game. Mostly because of personal bias for the Halo series, but also just because I tend to have more fun with it that I do Black Ops III. The Arena and Warzone multiplayer modes mixed with Forge and online custom games makes it the better game for me.