Couple of well regarded RIBs there. Subtly different - Ribcraft can probably customise ad infinitum if you are buying new, Gemini may be a bit more limited for console/seat choices (and you need to be happy with a rather lorry-like steering wheel position on their double console). The Gemini has, I think, a fully moulded deck and a largely wood-free construction. The slightly longer boat may offer a little more comfort.
P'raps also consider Humber Ocean Pro, but take your time choosing and do a sea trial - it's amazing how different RIBs can be.
Are you looking at new or used RIBs?
(You should also look at Tornado http://www.ribs.co.uk
/ XS-RIB http://www.aboard.co.uk/remoteurl?ht....xs-ribs.co.uk
loads of satisfied customers)