Paying for grad school...loans vs. savings vs. 529?

Hello, I am currently working full time while pursuing a Master’s degree part time. I’ve already paid for my tuition up to this point with my savings and with contributions from my employer. Now I’m wondering which option makes the most sense to finance the rest of my degree. Options I’m considering:
-federal student loan
-private student loan from credit union
-401k loan (I’ve read a little bit about this, and it seems advantageous because I’m essentially paying the interest back to myself…but wondering if there are any disadvantages to this.)
-personal savings
-set up a 529 (I do not currently have one) and move my savings into this account, then pay out from the 529 (maybe this does not make sense because I would not have that much time to realize gains?)

I would appreciate any insight into the advantages or disadvantages of these options. Or maybe there are some other options I’m not considering. Thank you!