I am using a Oneplus 5T, but best supported currently are probably the volla phones that come with Ubuntu Touch preinstalled or the fairphone 4. Pixel 3a is also a good choice. But yeah you won't be using the newest flagships on this OS, which is fine for me, but may be a deal breaker for some. You can check the exhaustive list of all devices and their current status here: https://devices.ubuntu-touch.io/