If you're looking at tiny boards, then I'd check out the ESP32 based boards right now. Cheaper. Personally, I think the R-pi Zero is quite attractive due to its lower barrier of entry.

Also, consider creating your synth/audio processor on your local machine first. Tweak all parameters. Make it perfect. Then port to hardware + UI. Not the other way around. The times of fixed points maths/DSP optimisations driving your algorithms are behind us.