My experience is different to Jack's (and oft repeated on here
Over my last few petrol cars, from various manufacturers, I have done testing on a brim-to-brim basis and found around a general 8-10% improvement in consumption using premium fuels. However the extra cost means no money saving, but more miles in the tank. Currently I am using Esso, but have found a similar effects with both Shell and BP premium grades.
The differences to Jack may be down to driving styles, diesel vs petrol, or type of journey; so the only thing I can say is to carry out your own tests for about 1000 miles on each after the engine has bedded in, and make your own decision. It may be worth it for extending range in the tank. For the reasons I have given, I would not expect it to save any money, but you have nothing to lose except the cost difference on a few tankfulls.
Incidentally, there was an 'Honest John' letter in his newspaper column on this subject in the last couple of weeks; where he states that he believes manufacturers set up the ecu's to be optimised on premium grades of fuel. I can't say if that is right, only give my personal experience.
I'm very much in favour of shell v power - years ago it transformed a Nissan almera from 'stodgy' to 'sparkling' performance .... so I've done a tank fill from time to time and I can 'feel' the difference apart from a modest improvement in fuel consumption