Osu! Tatakae! Ouendan

It has the weakest gameplay in the series (a lot of spinners, for example) and unskippable into cutscenes, which are very frustrating on higher difficulty levels since you will be re-watching them over and over again. However, it has the best music in the series by far. I recommend you purchase the cart and then legally back it up to your computer. Then, run it on your DS using a flash card and use save states to skip these annoying sections.