What's the best strategy?

[Christopher Piper]

My wife and I have a rental with a 3% mortgage on it that nets us $300 a month.  We also have our personal property that would accommodate us putting two bedroom, one bath rental spaces in them.  

We're considering selling our current rental to finance these spaces with no loan.  In return it would net us 10 times our current profit from the single rental.  Or we could use the Heloc money we already have to finance this project.  Our profit wouldn't be nearly as much and have interest to consider. 

What would be the smarter move here?