I use a number of mapping service quite often. Streetmap is the only one of the big ones that accepts OS grid references (and it can display on an OS 1:25,000 and 1:50,000 map). Other than that it doesn't provide much, no directions, no satellite imagery, it hasn't really moved on in 10 years of using it.
Here maps gives has many of the same features as Google maps but has much more up to date satellite imagery for many places that I look at and has a great offline app mapping app for Android.
Overall Google gets my vote, even though its satellite imagery is often extremely out of date 10 years+ old., and it doesn't recognise grid refs. It has a good terrain, 3d view, the 3d buildings look great, directions and traffic information seems to be some of the best in my area (better than Waze, but doesn't have the real-time alerts of Waze). However it is becoming impossible to get get updates approved on map maker so a lot of data is getting stale.