asda is ok, apart from the fact I've been unable to get the internet to work...
I'd say O2 is the best depending on how much you top-up and bolt-ons.
I top-up £10 per month and get:
- 300 free texts
- 1000 free mins or texts to 10 favourite numbers (costs £5)
- £5 left to spend on calls to other networks/landlines/O2 numbers not in top 10/additional texts
All depends on what you want/need