I'll start.
I think research impact is an overrated statistic. Uni applicants go absolutely crazy over this one and people often rank universities based on this stat alone. This stat has the obvious flaw of failing to take into account university size. It turns out that the higher universities are simply bigger and therefore have more research throughput. Research impact also has negligible impact on the quality of teaching at university. Some professors who are great researchers aren't great tutors, and vice versa. Research impact also doesn't influence the course structure, which is a critical topic for an applicant to consider.
I think student satisfaction is an underrated statistic. Just a single mention of the term gets people turning their noses up and sneering at you. But university is a very difficult time, and stress, anxiety, and mental illnesses are common. It's important that a university has systems in place to help students through tough times, and that the university and the region it is in are enjoyable and active places to study for 3-4 years. If you don't enjoy your time at university then you won't achieve as high as you should, and you won't have the time of your life like university should be. You could just be spending the days, weeks, months, and years wishing it was over. Student satisfaction is in my opinion one of the most important stats to consider when applying to university. It factors in every aspect of university and is decided by the students - by people just like you.