I’m with EE for both my phone and iPad and have a no problems with a signal with either, though the iPad can get a 3G or 4g signal where the phone can’t 
My girlfriend has just “upgraded” to EE from Orange and in Europe she pays nearly twice as much for 24 hours data as I do
Isn’t it the case with a phone signal that it doesn’t depend on the distance to mast (generally) but the number of users accessing the system at one time.
Hence why it is impossible to text etc on New Year’s Eve?
That saiid I am with three and even in a city the signal comes and goes 
I have been an o2 customer for years, and had an inkling they could be in trouble last year.
They hived their excellent broadband off to Sky, and lately the phone network and mobile broadband has been a little dire, (Dropping calls and no signal and slow internet.) and I put that down to lack of investment. Sadly for me, I have 12 months left on my contract, but it would be interesting to see what 3 will offer us at takeover time to switch, much in the way Sky offered us sweetners to stay or go at the broadband takeover time, because I was a 3 customer in their early days and they were ■■■■ and got well slated because of their poor service, and Bombay call centres.
Ken.