I have no good reason to avoid Keccak. As far as I know, it is safe. It did win SHA3 after all. On the other hand, all SHA3 finalists were deemed good enough, and the reasons for Keccak's victory was in part to promote diversity —which I can understand. I couldn't just ignore the other finalists.

I've heard that Blake was faster than MD5, and just as safe as Keccak. That decided it. I'm glad I did it, because the code is simple, and turned out to use the same ARX design as Chacha20.

Now I can imagine using Keccak instead. But then I'd be tempted to base the entire symmetric cipher-suite on the sponge construction, to share code and cryptanalysis.