i switched to giffgaff 2 years ago from 02
giffgaff use o2 network but offer a hell of a lot better deals
its all done online
if you order a pay as you go sim from them and click my link we BOTH get an extra £5
only place i have ever had an issue with coverage is near the tops between ozzy and blackburn thers a spot that a call will drop as im driving down the road but it does it on my mates EE as well
anyway if you want to check giffgaff out look up their website and use the following link to order your sim and we both get a bit extra
https://www.giffgaff.com/orders/affiliate/goodburner