Seeking advice - Refinance Rental or Borrow from 401k?

[Jeremy Mahan]

I currently own one rental and would like to acquire another one in the near future.  I am trying to save up the funds for 20% down on my next investment.  To get the 20% I need to get my next property, I could borrow money from my 401k or I could possibly do a cash-out refi on my current rental property.  I'm not sure which is the better option.  I'll have to pay back any cash I borrow from the 401k, but I am not charged interest, however, if I do a cash-out refi on my current rental, my cash flow will decrease on that one.  Any advice you might have on which option is better, and why, would be greatly appreciated.