I walk through John Lewis chocolate section every day and keep a close eye on it (and regularly spend the last of my money there) so I am well aquainted with the choices you are talking about
Last year I gave up chocolate for Lent and by the time Easter came I had stocked up 13 eggs in my wardrobe. Oh the shame. I would recommend Hotel Chocolat, their eggs are amazing. "You crack me up" is the one I'm going to buy myself this year And I'll hint to my mum that I would appreciate the eton mess egg sandwich. Yum yum. Every year I get the same..."are you not too old for an easter egg now?" NO MUM. I don't care if I'm 23, I still need an egg.
James chocolates look pretty but are a bit hit-and miss - not really worth the money usually. Their white choc is good though.
Charbonnel et Walker is good for champagne truffles but apart fom that, nothing noteworthy.
Cocoa Bean Co. is pretty good.
Godiva is nothing special, wouldn't bother going there if I was you.
Also in John Lewis you can get Rococco and Cococo - both of these are fantastic companies. They are pretty pricy but I think it's worth it. Personally I'm waiting til the day after Easter when everything will be half price
Gofre is right, Hotel Chocolat totally own this game.
However, I saw the most AMAZING Easter Egg in the Choccywoccydoohdah shop in Brighton a couple of years back. It was humongous and decorated really intricately - a thing of pure beauty. I haven't got a picture of it but here's a similar (not quite so beautiful) egg they made to give you an idea of the size. Unfortunately it had a suitably ginormous price tag to go with it... it was £750!