It doesn't really matter on blades edge or dalaran, if they are smart there is really nothing you can do to stop them from kiting you.

In blades edge I never go up top, but the other group can stick people up there to free cast etc. On Dalaran I am not sure which I prefer, fighting on the platform, or trying to pull them off the platform and fighting on the edges, I've had success and failure both ways. I think fighting off the platform is best, since one guy can totally screw you over by jumping off and pulling a couple DK's off with him. Then to get everyone back on DPS you gotta run down collect them and run them back up.