Kobo is (IMHO of course) better in all aspects except that they make it hard to migrate to them. Yes, you can manually copy epubs / kepubs, use Calibre etc but they don't have a cloud for managing your existing library or sync your reading progress. You always have to use workarounds for synching like
https://kobli.me/ that may just stop working or reach the end of life.
Amazon at least gives you the option to send them epubs as documents, pocketbook has a 5 GB cloud for existing epubs, Tolino offers 20 GB for existing epubs IIRC. But Kobo doesn't do any of that.