Tesco mobile are terrible. I had to switch as the internet was so poor. Im still on them for calls on a different sim fitted into a gsm alarm dialler but the internet is unusable.
Vodafone is a much better network, better than Eir/Gomo , their internet is rock solid here and in the UK and not too expensive either on prepay, Vodax is 20 for unlimited internet (fast enough theres no buffering at 1080 when tethered)/texts and 100mins, I think its 30 for unlimited calls and texts and internet. I run a gomo sim in another slot on my phone( for unlimited calls @10e a month) so can compare the two.