Not a fanboy thing. Just one very specific reason that matters for me.
I have both. My work phone is an iPhone, my personal is a Pixel. I've played Sideswipe on both. Ask me which is 'better' and my honest answer is: iPhone is smoother out of the box, and I still prefer Android. Here's why.
On Android, I can map a controller with Key Mapper. On iOS, I can't. That's it. That's the reason. The whole app.
iOS has native controller support in a lot of games but Sideswipe isn't one of them — Psyonix has said 'no plans' more than once. So if you want gamepad on iPhone you're waiting on them. On Android, we just… made it work.
There are trade-offs. iOS has better haptics. iOS Sideswipe has less input lag in my testing (like 10-15ms less, which sounds tiny but you can feel it). But those don't outweigh actual buttons for me. Not even close.
If Psyonix ever adds native controller support to iOS I'll probably reconsider. Until then, Android is the only real choice for controller players.