Hi Jim
I've had a Vodafone payg sim for about 3 years now, good signal and you get free extras like minutes when you top up, my neighbour has orange which also has good signal.
If by any chance you are on 3 in the UK (I am) from April 1 there are including Spain in its feel at home destinations which allows you to use your phone as if you were back at home, I get unlimited everything so I can call, text, Internet while out there for nothing.
HTH
Regards
Richard