If you want something you can get a bunch of for cheap, Kitty String is awesome. I, however, LOVE the Toxic BG1’s. Alot of the “high quality” strings last much longer than normal polyester string, and many times play better too. These strings are also built as “specialty” string; meant for a certain purpose, like whips and slacks.
Another thing: String doesn’t have too much to do with responsiveness. That is mainly the yoyo and the response. But, there are ultra-thin strings made for extremely unresponsive play, but I find that there is not a huge difference besides the slippy binds that the thin strings offer. String really doesn’t determine what tricks you can do. It’s your skill, coupled with the yoyo. If you have an unresponsive yoyo, you can do Spirit Bomb on 50/50, Polyester, or even cotton.
Chaos would be a good option, but the company is so unreliable. It takes months for them to ship out your order.