I'd consider switching to an iPhone, but lots of my music is just MP3 files and I'd hate to lose the ability to play them on my phone. Using iTunes is not an option.
Yeah iTunes makes transfering libraries or switching PCs unnecessarily tedious. I've had a lot of problems with it. I also think Apple's product decisions (hard- and software-wise) are becoming more dubious, which is why I was looking to switch. Privacy and security still outweigh it by a wide margin which is why I won't switch for now.
As for the MP3 problem: There are 3rd party apps, where you can simply drag the files into the iTunes window and they'll sync without hassling much with iTunes.
Couldn't you just dump your files in VLC for iOS and play them that way? There are probably more tailored music apps where you could put your local music collection too.
That's possible, but VLC doesn't have a good UI for browsing your music library. Grove Music was good at this, but it was bought by Microsoft and imho has since regressed.
There are several 3rd party options for playing audio files on iPhone without iTunes. The two I use most often are Plex and CloudBeats. Recently, I have been giving Bound a try for audiobooks instead of CloudBeats. I really want Plex to support some basic Audiobook features so I can use just the one app. The audio I listen to is stored either on my home server (Plex) or a cloud service of my choice (CloudBeats and Bound). I don't touch iTunes.
Disclaimer: I rarely listen to music. I'd wager 85-90% of my aduio listening is podcasts and I do that with Overcast. This may lead me to have the false belief that not using iTunes for music is easy/not a hassle on the iPhone.
