The Barnack Leicas are superb machines, built to the finest quality standards, and an exercise in precision to use. But there were reasons that Leitz came up with the M's and subsequently discontinued the screwmount cameras.
The M viewfinders are infinitely better. It's just not a matter of convenience: I will get shots with an M that I will miss with a Barnack because of the time spent in framing and focusing with the dinky little separate VF and RF. Based on years of experience with the M series, Leitz had the chance to update the Barnacks with a good combined VF/RF and a back door for easier film loading in the IIIG and didn't do it. And of course, I can still use all my screwmount lenses.
I will have to agree with many of the thoughts posted here about the wonderful little Bessas. I have both an M4 and a Bessa 3A, and I suspect I use the Bessa twice as much as the M4