Random orbit much better than orbital for anything other than fine
finishing, but if you need real bite then dual-action sanders have it
(at a price):

http://www.axminster.co.uk/category-...ers-206929.htm

(though in "turbo mode" they're really aimed at *shaping* wood, rather
than sanding it)

Selection of random orbit here, I can recommend the Metabo:

http://www.axminster.co.uk/category-...ers-206928.htm

You may want to consider the weight if you're using them on a vertical
surface.