I know of Salsa20 which won the ESTREAM competition. This is dated of 25 Dec 2007.
There is also the ChaCha20 stream cipher (cr.yp.to/chacha.html). This claims to increase the amount of diffusion per round. This is dated 28 Jan 2008.
Then there is another variant called XSalsa20 which has a 192 bit nonce instead of 64 bits. This is dated 4 Feb 2011. I'm not sure if it contains the diffusion per round improvements from ChaCha20 though.
Question is, which variant of these is the most secure to use? I do not care about speed. It would be really nice if cryptographers would just number their cipher versions/improvements as 1.0, 1.1, 1.2 so people know which is the latest algorithm easily.
On one hand, a 192 bit nonce with XSalsa20 sounds more secure than a 64 bit one. Maybe someone can explain the advantage of that? Would there be an advantage in using a 256 bit nonce which would keep it consistent with the key size? On the other hand, the better diffusion per round of ChaCha20 sounds like a good thing to have as well compared to the original Salsa20. Could a combination of the improvements in XSalsa20 and ChaCha20 be made?