I almost always add some red wine in my tomato based sauce, except for when I do amatriciana. I also prefer the red in Bolognese sauce although most of the recipe suggests the white. It adds a distinctive depth and a pleasant tang in the flavour, without which, to me, the sauce would taste a bit bland. I just glog it out on to the sauce and don't measure, but I would say about 100-150ml (3,5-5oz) roughly for 2 of us, and the rest we drink it off for the dinner, which works out well as the full bottle (750ml) is usually slightly excessive for us to finish it.
Our favourite red which is used most often is Lambrusco di Modena.