Tisri,
I've got a Rocky and it works great. Raf got a dodgy one it seems. IF you had a problem with anything made by Rancilio the advantage is that the CoffeeMachine Co. have a repair facility not far from London Bridge. I was there picking up some bits and pieces a week or so ago.
I see you are in London. If you want to have a look at things for yourself. I'd try the following places.
Fairfax:
http://www.fairfaxcookshop.com/ On the Finchley Rd (Nr Swiss Cottage) Has La Pavoni and Innova grinders in stock.
Selfridges: didn't find anything on the web and I presume you know where they are
. Has La Pavoni, Gaggia, Isomac and KitchenAid (possibly smaller Bodum as well) grinders on display.
Dury:
http://www.coffeemachinecompany.co.uk/ Much easier to navigate on! CoffeeMachine Co supplies Drury, but they are more or less the same company (just serving different markets) Has Rancilio and Mazzer, not sure you if could visit them for a demo.
To be honest, I'm not sure there's "one grinder" which suits everybody and all sorts of coffee "machines"... compromises have to be made (often with size/cost) and so you pick the best machine for you. If you want more detailed info, you'd have to explain precisely what it was to be used for and what you'd be looking to spend.
Hope some of this helps
D