I have both VLC and MPV and VLC used to take 0.5 second to seek forward while MPV being completely seamless. But I just tested again today and VLC has become seamless too with very minor differences. idk what changed
Edit: to answer your question I can't say much other than preferences. I like MPV because it's minimal, but VLC is good too
The problem I have with vlc is it's too minimal. I use the playback settings a lot and there are looping and playlist to enqueue videos. It's just easier to use and you don't have to memorize a bunch of keyboard shortcuts for a damn video player.
It seems hit and miss for VLC. I've used it for many years in Linux and can't pinpoint the moment when it became bad for me, but it now has difficulty to read a significant portion of my video files.
It lags when playing videos, or there is sound but no image, or it flickers. It just became unreliable for me. And if we google a bit, there seems to also be lots of people in that situation.
I tried a few things, changing settings and what not, but it never worked correctly again. Even on a fresh install. So I gave up and just use mpv now.
Edit: I just remembered. At one point it was not closing properly. Like, if you didn't stop the video playing before closing VLC's window, it crashed and stayed in the background. It opened new instances but every time it was closed before stopping a video, it would just crash and stay in the background. Eventually I'd have 4, 5 or 6 icons of VLC in my notification tray and would have to kill all of them. It was annoying.
I sadly had a similar experience. Worked for me flawlessly for years on Win7, but the moment I switched to 10 and there-after it has been a buggy experience with crashes, especially with x265 content. I had to switch to using MPC-HC.
A big reason I use MPV is because of anime. I forget exactly what the reason was back in the day, but I can remember MPV being better at playing certain formats, and fan subs of anime are early adopters of new codecs. In addition, there is a very healthy ecosystem of plugins related to language learning, which again ties back to anime.
All my life when I have to use vlc or try to there's something slightly wrong or not working as expected. Mpv has always just worked perfect and right. Does one thing well: it plays anything you throw at it.
Both are using basically the same libraries and tech behind the scenes, so one should use vlc if there's need for the features it has, like the library and chromecast, etc.