It depends on what you want to spend your time doing when you graduate. The first two are mostly indoor laboratory setting jobs. GIS is mostly a computer-based grad program.
Engineering is a math and science based program.
Since you have a biology degree, toxicology is the best fit for you of those majors, and will probably require the least number of classes. Don't forget that a grad program can be a part-time job too, so it is not like you are just in school. All rights reserved.