The best way to check the signal in your area would be to just pick up a pay-as-you-go sim, put it in your phone and take it with you to the places you're at the most to see if the signal is any good. I'm currently with Three.
I have been with Vodafone and Giffgaff (O2), both of which were total crap. I had a friend on EE who kept having issues with signal drop-outs and the abysmal customer service, recommended him to Three and he's been happy ever since. Just try what i suggested above to see if Three/EE is any good for you.