I think I have used all the maps now that you can use on a 705/800. The views I have are from predominantly a road users and never go cross country, apart for the very odd occasion.
The OSM maps from the following website are the best that I have used:-
http://garmin.na1400.info/routable.php
The OSM maps from the following site I also use and like wise are very good, but they do on occasions have a tendency to route me across country, where no track or path exists. The contours from this site I also use with the OSM maps from the above site.
http://talkytoaster.info/ukmaps.htm
The OSM Velo maps I gave them one go and found that they would alter my course which was designed only on the road to go cross country and make a mess of everything, untill I changed back to another map, and then the course would go back to road only.
The Garmin Metroguide and city navigator is also very good and use quite often, but sometimes I like a bit more detail, which the OSM maps can provide.
The OS dicoverer maps I have just started using, but I find that the information at times can be a bit overwhelming, especcially in towns and cities etc when you are trying to spot what road you need. The pink line can be lost amongst all the background clutter, and when you get the zoom in map, I find the screen goes black, with just a white arrow and you see your position move up the arrow, workable but not ideal. Also when you zoom in, the detail becomes very large and blurred on the screen, unlike the others, which seems to keep to a modest scale and in focus on the screen. The OS maps will auto route and are more ideal for cross country navigation, and slower paced touring etc where you do not have to make snap decisions where to turn.