If only one bike…
Something like a Stooge with rack and guard mounts, gears, and option of a + front wheel plus some c. 40mm file treaded/all round tyres for road to towpath stuff. I think it would have Jones or some other weird shaped bars too. It would i suspect be a compromise for road/sedate stuff but plenty capable enough for 90% of what I do.
That and something with drops would be better = two bikes.
I still wonder if I should have bought a Stooge instead of my FS bike. Something very appealing about them.