Compared to IONOS, it is day and night. IONOS in my experience is just worse in every category that matters. IONOS has buggy and bad wannabe SPA web frontend, broken OS images, bottlenecks in their provisioning API, that they don't care to fix, and 10x the costs.

If you are not desperate for one specific offering of IONOS, that Hetzner doesn't offer, and you have any other options, there is no good and justifiable reason to go for IONOS. IONOS is a low effort, low quality, high marketing spend shop. Hetzner is almost the opposite. They don't waste money on advertising, they cost much less to rent servers from, their OS images work, they got good technical support.