When I did have my landline, I never had one issue with the service in the 25 years I had it.My landline was terrible. Rural area, lots of old cabling and moisture getting into the line. Crackles, echos, and fading in/out.
My cell is crystal clear, especially when calling other guys on the same carrier where they enable HD quality. But then there is the issue of the occasional drop outs, so it really depends. There are pros and cons to both.
Not much to go wrong with two tin cans and a long string.