Terminator has not been updated in 9 years, suggesting a lack of maintenance, and is stuck on GTK2, which means no native Wayland support. Tilix, on the other hand, is active, GTK3-based, and works natively on my Gnome Wayland desktop.
Not true. Terminator is still being actively development (albeit somewhat slowly). GTK3 support was completed earlier on in the year and I've personally been using it daily since.
Seems to have saner handling of saved/loaded profiles and color schemes. Also the session switcher seems nice.