Morning Ian,
The other way around for me.... I exclusively use Amplitube 3 for all of my recorded guitars. I am not a fan of Native Instruments stuff at all (Guitar Rig 4) - but as Alan says - it is all very subjective. The other one you may want to take a look at is 'Eleven' by Avid. This is an extensive and authentic modeller available in both software -
http://www.avid.com/US/products/Eleven - and a really great hardware rack version -
http://www.avid.com/US/products/Eleven-RackIncidentally - there is a free version of 'Eleven' in Protools 8 and later...
With the recent resurgence of VOX though - I don't think it will be too long before they choose to enter the software market with their own product...
Best always
Tony.