Is it better to use reference letters that show variety, or two letters from the same job that better fit the program I'm applying to? I am an undergraduate student getting ready to apply for graduate school in a few months.  I have worked in two jobs in Physics (my desired field), one in experimental and one theoretical.  At each job I have at least two people willing to provide reference letters, and I believe all of them would be good references.

Many of the graduate application websites indicated that 2 (or more) letters of reference are required.

When I apply to one of these programs is it better to double down and use 2 letters that apply to the same program (ie, use 2 references from experimental group when applying to an experimental graduate program)?  Or would it be better to have a bit of variety (ie, one letter from each group, regardless of whether I am applying to experimental or theoretical)?

I'm leaning towards the variety, because I think that two letters from the same job would end up having the said the same thing, whereas the variety gives the university an idea of my breadth of knowledge.
The content of the letter is more important than whether the author is a theorist or experimentalist.  I suggest you ask your letter writers what they think.  They will know if they will write you a good letter better than I will.