This phrase is confusing me. I know the "been down the road" means that you're familiar with certain activity or situation.. but what about the "longest" here..
could it be either a hard situation or a long term situation?
I'm afraid I cannot connect "the longest road" with being familiar with something.
I see from Google that this phrase came in the Irish song If I could choose, which was performed at the Eurovision Song Contest in 1967:
"If I could choose a place to walk with you I'd choose the longest road."
This suggests maximising the time spent with someone, something that would be welcome.
Where have you seen or heard this phrase?