There's advantages and drawbacks to either option. Getting yourself highly-leveraged (using all the HELOC) puts you in a risky position should you have unforeseen capital expenses, and no way to pay for them. Worse yet, since most of the country has seen positive real-estate valuation gains since 2008/2009, should another "correction" occur, your equity withdrawl may leave you underwater on the property. Couple that with a large capital expense, and your boat may sink.
On the other hand, another property is another property. Sure, if your only driver right now is short-term cash flow, you just have to compare the cash-flow of one property with a smaller mortgage to two (or three) properties that are all much more leveraged. (also take into consideration having to manage more tenants with the 2nd option).
But the beauty of the rental business is that, for the trade-off of managing tenants, you are essentially getting people to PAY YOU to buy YOU a new house. At some point, if all goes according to plan, those mortgages will amortize into thin air, and you'll own rental properties free and clear. And would you rather own one, or many?
I personally would take a middle-road. Leave enough equity to maintain a solid standing on the current property financials (to weather a large expense or market correction), but utilize the rest for acquiring new solid properties.
Good luck!