I've tried many, many brands of 300B's... Here is my personal preference...
1. Western Electric - the standard on which all 300B's are judged.
2. Takatsuki 300B - fantastic, does not do anything wrong.
3. Living Voice 300B - very close to the Western Electric 300B but with a bit more bass response (slam). The LV 300B's are made by Eunice Kron at KR.
4. Emission Labs 300B solid plate - Very good, but not as good as the Top 3.
5. Electroharmonix Gold Grid 300B - an absolute bargain and a real 300B that can take 450V plate voltage.
In my experience, there are many, I repeat MANY, tubes out there that claim to be 300B's but cannot take 450V plate voltage and will fail. Many do not come close to these specs... https://www.westernelectric.com/products/images/300b/300b-technical-specifications.pdf