When I was in your position years ago I took situation B, but before doing that I had good reason to believe I had a job lined up that was interested in the MS. My main reason for choosing B was I felt I’d never have the time to do a masters full time once I entered the job force, and I wanted do have a degree that distinguished myself. All of that worked out fine for me and I have a good job now.
However, looking back I would choose Option A. I didn’t learn a lot of new things from my Masters because there was so much overlap with my undergraduate degree. I would have appreciated it more as a part time program later in my career when I had more experience. Also, it took me 5 years to catch up with the salaries my friends who didn’t take the pause were making.
I’d recommend taking the job, work for 5 years then revisit the masters.