I'm due to get out of the military this year, undisclosed date, and have several job options lined up for me. 

I don't want to work too hard, of course, but I do want to live extremely comfortable. 
There are jobs that offer salaries from $40,000 upto $90,000 (USD, per year) that I am qualified for, and am considering applying for. 

What do you think is a decent amount to make, considering I will be going to school full time as well? (assuming that the amount of work one does at the job is relative to the pay)

Thanks.

Jason

Not to sound like an ass but make the most amount of money as possible.  Those people who say money isn't happiness are not entirely true.  90k would put you sitting rather comfortably and having most of your loans paid off AS you're leaving school (if you're smart about it).  If the job is not too stressful / time consuming there's no reason not to.  You don't want to struggle with money with the stress of a new job and school, that's just not "happy".

I'm assuming you are going to receive a grant from the government for your service in the military to apply towards higher education, so that should help tremendously.  Do whatever you are comfortable doing, at least for when you're providing only for yourself and going to school.  Once you're out of school, your military experience and degree should be plenty to land you a high pay job.  But don't bite off more than you can chew in the mean time, school and work simultaneously can be tough.

Yes, I am pursuing my Master of Public Health, and will continue when I get out using my G.I. Bill.

Jason,
Consider the costs of living in your area and the types of job you want.  If things cost a lot in your area, you'll need more money.  If you want to live comfortably above what the average is in your area, you will want to earn more money.  The amount of money you earn on a job is not necessarily proportional to the amount of stress/work.  Lower paying jobs can give a lot of stress.

You may want a job that is somewhat related to your Master's work to give you some job experience (and in the off-chance, you might discover it isn't the field for you).

From what I understand, all jobs are pretty much the same, since they require some interaction with other humans. It doesn't matter whether you work at McDonald's or Boeing - crybabies dominate the scene. So, do you want to be one of the crybabies or control the crybabies? You can't have it both ways, so you have to pick. After having been a manager for the past 3 years, I have noticed that everyone whines.

If you live in the midwest, your cost of living will be considerably lower than on the coasts. I'm right in the bible belt and my cost of living (totality of bills) is less than $1500 per month. My car is more expensive than my condo.

Personally, I'd fight for the $90,000 per year job. If you hate the job, just think about something else while you're there.
A work shift, unlike life, ends quickly.

Make as much as you can and put as much of that as you can in tax shelters like Roth IRAs and 529's (to help pay for your education).