It came down to who could provide a decent price for data whilst in Europe.
Only Vodafone and O2 offer anything that allowed data usage on an add-on. The others just had roaming.
On the plus side. O2 has better coverage at home. Yes, I actually have a strong signal and the dreaded "no Service" has yet to flicker up.
At work it's about the same.
And the cost? £16 a month instead of £36.