I have a Master's in Geography (w/ Remote Sensing and GIS emphasis), taught GIS labs, and really enjoyed the program and it certainly has opened some doors. Whether to do GIS certificate or a full Masters degree depends on your end goals.
If you want to do research, if you love the field of geography / spatial science in general, and/or you want to pursue a career in academia, teaching in higher ed, professor, etc, then go for the Master's degree and PhD. If you only want some add-on skills to augment a primary profession or other field like engineering, GIS certificate makes more sense.
I would caution that I've found most GIS jobs to be pretty low salary for those coming out of GIS programs into their first jobs even with a Master's degree which is one reason why despite having a Master's in it I haven't made a career change from my original professions. Even the academia positions are pretty low pay until you've been tenured somewhere. I say this because I see you are 1) in engineering already, and 2) talking about a career change. As an engineer combining something like an MBA w/ your undergrad engineering credentials may be far more lucrative than something like GIS. So I would just say if you do GIS do it because of interest and not because of the money, and if earning potential is a priority might be better combining a GIS cert with something like an MBA or Master's in Engineering, PMP, etc etc. That said there are some who've managed to do really well in GIS and of course that could be you too, ultimately you're largely the author of your fate.
As far as where to study I recommend first deciding between Master's or Certificate option, then deciding what discipline within Geography/GIS you want to pursue, and then all the other life considerations only you can answer for yourself like where you want to live. Different universities have different strengths...for example CU Boulder is great for Human/Regional Geography, UCSB is great for the technical/spatial sci side, I like Wisconsin's cartography, etc, etc etc. Then drill down to specific research and projects...look at the topics you're most interested in and then let that inform your decision on which schools to choose since different schools and professors are doing different research. But if you're only interested in the basics like GIS software, almost any GIS graduate certificate program from an accredited institution will do.
I had a great experience in my Geography Master's program at Western Michigan University. They had a China scholar there that I wanted to study under for my thesis research, it was close to University of Michigan where I was studying a different Masters degree, and they have more money for funding graduate students than most geography graduate programs due to a very generous endowment...when I was teaching GIS labs my tuition was covered 100%, I had a pretty decent stipend, there were many good research and teaching assistantships and scholarships, and even things like travel and registration for conference presenting was funded. The faculty and facilities were excellent too and it wasn't too large or too small. They have an M.S. in Geography as well as certificates in GIS and also Geospatial Applications in UAVs. Here are some links to WMU's programs:
- Master's: https://wmich.edu/geography/academics/masters
- GIS Cert: https://wmich.edu/geography/academics/certificate-...