Best way to finance a new purchase

[Pasha Gorky]

I am looking to purchase a 2nd rental property. My 1st rental is fully paid off and is occupied. I also have enough equity in my primary home to cover the purchase.
Should I do a cash out refinance on paid-off rental, do a home equity line of credit (HELOC) against the rental, or a HELOC against my primary home? 
I found a credit union that can open a HELOC at a 3.49% for the next 12 month which sounds very attractive.
What would be my best option here?