I've just gone with giffgaff and spent the last 24 hrs trying to work out why I didn't have 4g when the website said they have it.
finally managed to work out that it's currently only on trial to customers who were with them before March, the trial continues until October when they then launch to the general public.
4g will be on all the tariffs with a limit on data, I'm on an unlimited data one, so another reason why I can't get it.
Seem me to be getting H+ on my new galaxy s4 though, which is supposed to be faster than 3G anyway.
My biggest issue is being an apple person and having to navigate android, there's TOO many options, and they seem to be all over the place, just not at all intuitive. Like the big screen though, but not the woeful battery life because of it.