I wasn't very impressed with sync when I tried it out after all the hype: maybe because I've been a long time infinity user. I can't give a fair comparison since I haven't given sync too much of a chance, but here's what I like about infinity:

• FOSS, on fdroid (fdroid >> play store for me)
• nice UI - adjustable font sizes, top comment scrolling
• multiple account support
• dark mode is pretty dark (yeah, I really like dark mode)
• fairly stable