I've been narrowboating for the last couple of years and would thoroughly recommend a one way trip between between New Mills and Trevor. We did this trip as our first trip on the canals and thoroughly enjoyed it. Theres a good mix of scenery and to finish the trip, the absolute last thing you do, is to cross the Pontcysyllte aqueduct. An absolutely stunning end to the week. Theres plenty of locks and lift bridges to keep the kids occupied.
This trip was with Anglowelsh, who we have been away with subsequently and will do again in September this year, and I would thoroughly recommend them. The boats are kept in good order, they insist upon tuition even if you have been out before, and when we encountered a problem on board with a faulty water pipe connector, they were very prompt and helpful in fixing the problem. On our travels we've dealt with Anglowelsh bases at Trevor, New Mills, Bunbury and Great Haywood and we've had great service at them all.