Having travelled extensively over the UK for business purposes, I can tell you that I've only ever used the M6 Toll when someone else was paying. Using the M6 itself isn't too bad as long as you avoid peak times.

That said, and seeing our local motorways come to a standstill most days, I observe two things...

1) The motorways are over crowded and can no longer cope with the traffic density
2) The standard of driving in this country has declined rapidly

Sadly, I only see things getting much worse

I use the M6 toll when I head up to the north-west to avoid the worst of the queues on the main motorway, but it's coming to the stage when it's not worth the money: http://www.bbc.co.uk/news/uk-england-40521705