When I was 24 (in the last century) some friends and I hired a 55' long narrow boat for a fortnight.
Starting at Rugby we headed south down the Oxford Canal to Oxford. There we joined Isis(!), or the Thames and travelled down to Brentford, West London to join the Grand Union Canal, back to Rugby.
It was quite a demanding schedule and we set off early each day so we could max the time to absorb the culture at the excellent public houses along the way. I have memories of us working through locks with some crew members still in pyjamas!
The Oxford Canal was far and away the prettiest with very narrow locks, fractionally wider than the boat. These proved a challenge for the first day but the steel boat absorbed a lot of punishment.
The Thames was pretty and interesting, but not something you couldn't do over a series of weekends on a tour boat. The locks are massive and all electric and it was only when we manually worked through one lock early one morning that we appreciated that power.
The Grand Union was more industrial and interesting from an industrial archeological perspective and pretty in some places. The locks take boats two abreast and are much bigger than those on the Oxford Canal. A highlight was a magnificent flight of locks, from memory somewhere in N. Northamptonshire, where we spent much of one afternoon working up and and over a hill. And of course Blisworth Tunnel which, from memory is a couple of miles long - and we didn't try legging through it, but it was a good experience.
I have no idea how congested the canals are now but I would be happy to have another canal holiday if the opportunity arose.
