You won't get a definitive answer to this question! I've had a bad experience with EE and will never use them again. Ive been a happy Three customer for over 2 years now - their signal can sometimes be patchy outside of the major cities but as a Londoner it meets my needs perfectly.

For £15 you can get a PAYG SIM which will give you unlimited data, 300 mins and 3000 texts.