Msi twinfrozr - £501.95
Vs
Gigabyte windforce (slower one) - 491.99
Vs
Gigabyte wf (faster one) - 532.00
Vs
Evga sc acx - 519.99
Vs
Asus directcu II - 491.99
Vs
Zotac oc - 455.74
If one brand is supported better where you live, I might go with that.
In the US, it is evga.
Mostly the higher priced units have fancy coolers that are not really necessary on the GTX780 cards,
I would look for the evga GTX780ti superclock with the stock titan cooler like this: http://www.evga.com/Products/Product.aspx?pn=03G-P4-2883-KR
The blower cooler gets heat directly out the back of your case.
I was thinking about either msi or asus. Asus because alot of good peoples opinions and msi for good price and high clocks. Ive used evga 750ti and i must say its really good.