The problem I have with Snap is that it's a rather mediocre over-engineered technology (e.g. decompressing images had poor performance for a long time; see the Firefox snap drama) that is pushed very hard by Canonical. It has a closed-source market and nobody knows what Canonical does on their side for performing anti-malware scans (that haven't been very reliable in the past). That's not how open-source works. We want to have a decentral approach like Flatpak repositories have.
Flatpak is my default, but sometimes I also use AppImages.