I would start by taking a long, hard look at reputable college rating sites like the College Scorecard, a service of the US Dept of Education -
https://collegescorecard.ed.gov/
When I was looking at DD18's choices, some of the things I thought were important were
graduation rate,
freshman retention rate (% who stay more than 1 year), location, and diversity.
I have visited all four of your choices, and live within a 15 minute drive of both FIU and UM.
My DD18 has participated in an 8 week biomedical research internship at FIU, and it was amazing. She also attended a week-long Duke TIP camp at Eckerd that was very good, but it was presented by Duke University which is one of the finest universities in the US.
In addition,
DW is a UM graduate (communications), one of my
daughters is an FIU graduate (education), and the friend in Alaska I referenced in a post above is a
Marine Sciences graduate of UM and a career marine biologist for NOAA. I don't know enough about Tampa and Eckerd to really give you any advice.
UM and FIU are both
very good universities, and they share an amusing history. UM used to be known as
"Suntan U," and FIU used to be the
"Oh well, I guess I'll just go to FIU" school.
But they have both changed enormously since those days. Today, both are rock-solid academically, have very good reputations, and both are very competitive.
Of those two -- all things being equal, and they are not -- I personally would choose UM.
I say that because of the strongly established marine science reputation and the overall quality of the school. The downside would probably be that a lot of UM students come from wealthy families, which could be a negative or not. It's great if you like to Uber over to South Beach for a casual lunch, but not so great if you can't afford to eat.
FIU is a very fine school, and is getting better daily it seems. Florida has 5 really good state universities and FIU is definitely one of those five. The other four are
UCF (!), UF, FSU, and the University of South Florida in Tampa (USF).
The downside of FIU is that a large majority of the student body are local kids, and that creates a heavily-weighted demographic. Academically, FIU doesn't give up much to UM (and in fact, they have some dual-enrollment students who take classes at both universities), but the
"college experience" would probably be better at UM if money is not an issue.