I would like to urge the Japanese government to step in and sort this out, every year there are too many festivals happening on the last weekend of August: Koenji Awaodori, Asakusa Carnival, Super Yosakoi, Azabu Juban Matsuri, Roppongi Bon Odori, etc. All of them are unique in their own way and I am sure many of us would love to visit them all. It is a tough call to pick which to see under such a limited time over two days. This year, I did not go the major ones such as Asakusa Carnival or Koenji Awaodori, but let me share my thought/ experience of the two I had a chance to drop by. I hope this will be helpful for your decision next year.
Azabu juban Matsuri
The attendance to this festival is by default since I live in the neibourhood. This is not a usual japanese matsuri (festival) full of typical yakuza food stalls (i.e. colorful stalls selling karaage or okonomiyaki around the shrine) but a dining delight since most high-end restaurants in Azabu Juban will be selling their gourmet food. I am very impressed with the food quality such as grilled lobster, lamb chop and 500-yen red wine from a wine shop. All kinds of alcoholic drinks you can think of will be sold at this festival. The competition is fierce and the queue is crazy, but it is really worth it! The packed main street is catered towards 'grown-up' audience while the park in the middle of neibourhood offers some gold-fish scooping and other activity for kids. Festival starts at 3PM, I suggest arriving early to scout the stalls and prepare to queue up.
Omotesando/ Harajuku Super Yosakoi
If you lack energy, more than 5,000 enthusiastic danders from 100 teams performing on the street will surely revitalize you. Although it may not be as historical and cultural as the legendary Koenji Awaodori, the vibe around Harajuku/ Omotesando is full of colours and positiveness. I personally prefer to arrive early (e.g. 1030- 11AM) and walk around the event space of Yoyogi Park as well as the street leading to NHK to capture performers' preparation while being able to see the real actions at the same time since it is the beginning point of the show. The event spreads over both Saturday and Sunday, it is probably good enough to hang around for a few hours to grab some good shots and move on to another festivals on the agenda.