All the health insurance companies are pretty good. In a recent consumer survey, even the least satisfactory company was rated as good or excellent by over 80% of respondents.
Value unfortunately depends upon your own values.
As I have said before, read the small print before you sign up and make sure you have a policy that covers what you need.
Best value for most is probably represented by a hospital and specialist test policy which leaves you paying only a smallish excess and GP visit fees but covers operations and outpatient investigations.
In the end I got advice from a financial advisor, all for free, and was able to choose from several policy options with various excess levels. He was also pleased to offer advice as to which option he felt would suit best (in the end we disagreed but that was no problem!)
A word of warning though, these people can be very intrusive and will pester you a fair bit unless you ask them not to.