virgin.net like any other isp has good and bad happen with their service and their customers.
At the end of the day the adsl they provide is supplied by bt as it is for
the rest.
It comes down to contracts , customer service and technical support as the
only real differentiators.
Decide what you want, compare the different providers under those
headings and choose which one to go with.
But do read what is offered carefully.
Taking virgin as the sample.
There is no 12 month contract but if you leave within the first twelve
months you will pay a £50 cancellation fee.
Technical support is 25p per minute, their call centre is in the UK
Their customer service number is an 0870 national rate number, that callcentre is also in the UK.
Cannot comment on the quality of their customer service or technical support.
Check those out with as many people as you can.
The reviews can be helpful but remember people who have had a bad experience tend to write them more often than people who have had a good experience, plus I couldn't help but notice that one of them was actually about virgin mobile rather than virgin.net.