I like 4x4 the most because I have the Vin 4x4 UV - it is very nice to turn - and because I have been practising it lately, so I am faster at it than the other big cubes (also because the only bigger cube I own is a cheap, no brand, constantly popping 5x5...). Here is a VERY hot take on why I think I might like 4x4 the most. It is not only because it is the fastest big cube for solving, or that the hardware has advanced very nicely, but it is -----
The 49 different even-big-cube-only OLL and PLL algs as well as the 4 L2E algs!!! The reason why I like these so much is because I just seem to be stupid and enjoy learning loads of cool shortcuts which would otherwise always be the same boring, repetitive step. I've already learnt the L2E algorithms (they are very easy to learn), and I want to learn the PLL parity cases + maybe a couple of the OLL parity ones. Either way, 4x4 is amazing!