My GB bucket remains firmly centred around Sunningdale (both Old and New), although Lytham, Birkdale, Turnberry, Western Gailes and Cruden Bay are all clear gaps too as is Addington inland. Ireland is a massive lacuna, with the distinguished exceptions of all three Portrushes (although I haven't seen the new holes in the flesh), Portstewart and Dollymount. So RCD, Portmarnock, Lahinch, Ballybunion, County Sligo and County Louth would all be on the list, as would Ashburnham, Prestatyn, North Wales, Tenby and (of course!) Welshpool in the principality.
As for a Top Five achieved, leaving out the current Open rota then Prestwick, Westward Ho!, Alwoodley, Macrihanish and Brancaster will always loom very large, as will (to cheat) Silloth, Deal, Formby (Men's and Ladies) and Rye.