Been with 3 for long time, near 10 years.
The unlimited data on the one plan is brill and loads of mins and texts for your money.
But as already said if you go out of 3g signal you will have no internet as 3 no longer use another provider for 2g signal, its a fairly recent thing. That's no issue if where you work or travel too or visit often has a good 3g signal. I have good 3g signal at home, but I use my WiFi at home anyway, its when I am out and about it can be very annoying.
I am quite sure I will be moving to another provider when my contact is up