Based on my experience, and suitable for beginners (high performance but not too expensive).
1. Low grit: Atoma 400, for repairing or creating new bevel and lapping stone.
2. Medium grit: Suehiro Cerax 1000 (soaking), or SP/Kuromaku 2000 (splash and go).
3. High grit: Suehiro Ouka 3000 (soaking).