I agree, I was willing to give them a try if the price/tariffs where right...
That's not the case though, and as you said the O2 network is woeful in my experience, having signal is great but not being able to do much with it sucks.
Currently on EE and despite a few small issues and the lack of coverage at my mothers it performs very well.
I soon to be out of contract with EE, I considered trying Vodafone's sim only but for some reason I can't get through credit checking process with them.... weird considering I didn't have any issues with EE (Who'me I've had 2 debts with in the past and have an outstanding Orange account even still) I also got Apple's finance on the iPhone 7 without any problems.... anyway the experience with their customer service put me off recently anyway.
Hopefully EE can offer me something decent for a sim only.
Sky's long and annoying launch has been disappointing... I actually reckon that if it weren't for their potential mobile launch that I may have been in favour of an alternative Fibre provider (not that I have any issues with their BB)
Connected by Sky Fibre Max.