How to compare two CSPRNGs?
The best one is the most reputable one. That is, the one which had been widely used, studied, and standardized.
If both fall into that class, choose the one which uses more secure or larger-state primitives under the hood.
Example: when comparing the NIST-standard Hash-DRBG using SHA-256 versus HMAC-DRBG with SHA-1, I would personally choose the first due to larger state and security margin of SHA-256.