I've had EE before on a work phone. IT was shocking, i seemed to get 3g most places (sometimes 4g) but i could barely make a phone most of the time. Used to use my personal phone.
Might pickup a three sim and see how i go.
Can't say I've had many problems with Three. I occasionally drop off the network and have to reboot my phone, but I'm pretty sure it's a handset issue - I've never really bothered investigating it. I went with Three because everyone rated them for data speeds etc. I hope they're the same with 4G...