Cash or HELOC for Rental Balance?

[Bradley Benson]

Currently have an outstanding rental property balance of $40k, via 10-31 exchange (prior property paid off). I'm trying to decide on using accessible cash or taking out a HELOC on our primary home to payoff the rental.
 
HELOC would be a fixed rate of 6-7% on a  10-year term. 

My thoughts...taking out the cash can potentially hinder future opportunities such as a house flip that I could use the cash on. The HELOC could be utilized more wisely in other potential investment situations.

Any other suggestions?