#2 Brock Lesnar
If we are absolutely honest, this feud is probably the most farfetched idea of the lot, simply because of the sheer size difference and fighting styles these two competitors have. Brock is a raging powerhouse and Rousey is a technical expert.
However, that being said, both Rousey and Lesnar share a UFC background and are very similar when it comes to the 'fear' they fill their opponents with when they're with them in the ring.
A possible storyline could be woven if Rousey decides to become a Paul Heyman Girl, something many fans would like to see. It would be awesome to see Rousey take up a sort of Chyna role and throw around the Beast, but that seems impossible.
This all hinges on whether Brock is still here after Summerslam though, but even then it doesn't hurt to fantasize.