As background information, I am planning to apply for master's programs in Computer Science and do not plan to move on to a PhD.
After several years of drifting, I am finally on track to graduate this Spring. However, my program is completely online. I am doing research this summer so I will have a letter from that, but my other two will likely have to be from professor's I've interacted with only online. That said, I am a good and active student so I wouldn't expect these letters to be bad, per se, but given that classes are only 8 weeks long and the courses are online, I wouldn't expect these professors to be able to write the strongest letters either. I have a previous employer who I worked with for several years who would undoubtedly write me a very strong recommendation, but the work was in a completely unrelated field.
So basically my question is: do I stick with 2 possibly mediocre academic letters in my field of study, or replace one with a very strong professional letter in a field unrelated to my field?