Plotting my recommendation letters

I'm starting to take prerequisites to apply for a second-degree BSN. Because I've been out of school for a few years, and my courses were in a completely different field, I'm hoping as time goes on to find some professors who can write recommendation letters for me. I'm also trying to figure out which courses to take online. I'd prefer to take them all in person, but because of course availability, my work hours and cost, I'll have to settle for online for a few.

So, as I decide, I was wondering if it makes a difference which professors from which courses write letters? I was assuming the hard science classes, such as anatomy or chemistry, would be best. But what about nutrition or developmental psych? At the same time, it seems like getting a strong letter might be the most important thing.