IN general, yes, use the toll But it's only worth it if the traffic along the non-toll M6 is heavy.
My brother lives in Macc, so we use the route a couple of times a year.
From Kent, use M25, then M40 up to the M42 (round the north of Birmingham.) As we join the M42, we tend to check on Google maps what the traffic is like along the non-toll road.
We expect to use the toll, but if the traffic is light on the non-toll road, then we make that decision according to information from Google.
On a Saturday just after lunch, you might be OK, but check with Google. If you don't have that, or want to make that decision ahead of time, definitely take the toll road.