I use all the above mentioned maps, plus the Velo map which has not been mentioned:-
OS map, excellent out in the country, but in built up areas etc, absolutley rubbish, far too much detail which overwhelms the route your trying to follow, plus it is not helped by the Edges pink line your trying to follow for your course blending in with the map. After getting lost a few times in succession last week and not being able to spot my course on the edge of Hull, I had to switch to one of the OSM maps which only had the roads and the course I was following and not every little bit of detail imaginable and then realised how good they are.
As for the Velo map itself, it has a tendency to alter your course your following across country for some unknown reason which is no good if you only ride on roads, change back to an OSM, Garmin or OS map and your course switches back to road only, but Velo map may be Ok for MTB'ers.
Out of the OSM maps I find the following the best:-
http://garmin.openstreetmap.nl/
But the one mentioned above from:-
http://talkytoaster.info/ukmaps.htm
is also good but find it also has a tendency to want to go across country sometimes, but what I like about these maps is they have contours as well, but you can also just download the contours and use them in conjunction with the other OSM map above, but it does not always work for some unknown reason.