I only stayed two nights at K's and it was a little quiet as the hostel had only just re-opened after a refurbishment. The staff were super helpful with really good English, room was clean (but a little cold). It's just by the underground train station so easy to get around.
I really enjoyed my stay here - the couple that run the guesthouse are very friendly and helpful. They do have some rules and regulations but the house is obviously their pride and joy so I don't blame them. There are a lot of rooms all squashed together upstairs in the house and the walls are very thin so you can hear everything. Also if you have large luggage it's quite tricky to get it up the stairs and to find space to open it in the room! Disappointing lack of cooking facilities.
I really liked the funkiness of the hostel and how helpful the staff were. The kitchen area is really, really small though and not much fun to cook in. The atmosphere in the communal area downstairs was pretty friendly but the two nights I stayed there, the staff were playing Japanese manga which might not to everyone's taste or understanding and also limits the amount of conversation that takes place. It would have been nicer if they had put music on instead.
I had an enjoyable stay at Jimmyz; the owner, Jimmy, is extremely helpful and providing valuable information on places to eat, transport, etc. and also in general about Japan. The hostel is small and quaint and has a character of its own. A great place to stay and meet other people.
Very nice stay at this hostel - staff were excellent - really friendly and very knowledgeable about local area, things to do and how to get there. The cooker was out of order on the floor I stayed on which was a bit of a pain as there's only one kitchen per floor but apart from that everything was great.