You have used home equity lines of credit to purchase investment rentals and want to know the best way to pay down the HELOCs.Between the two properties you bought, after expenses, you have $250 a month positive cashflow to use.What I like to do is pay down some principal every month with my positive cashflow.I use my extra active income from real estate commissions helping other investors to pay down the principal even more which just frees up that credit for me to use again.I know I can refinance the HELOC debt before it changes to principal and interest as it is just interest only payments as yours are.One difference is the cashflow, I have greater positive cashflow and could make the principal and interest payment in the future with the extra cashflow I already enjoy.I always get HELOCs on my income properties as well after purchasing them to pull out as much of my downpayment as possible.

Start to evaluate deals based on the income approach and you'll do much better long term investing. 

To fund your next deal, explore conventional loans (15-25% down), FHA loans (3.5% down for house hacking), DSCR loans (based on rental income), or HELOC/cash-out refinance if you have equity.

I invest with PPR and other income funds through my IRAs.

I would underwrite buyers based on stability of income, financial payment history & ability to pay.

They are exceedingly rare, thus very expensive, but I believe they represent an excellent long term steady income and store of value.  

It lets you focus on managing the property and getting steady income right away.

@Thomas FarrellRecommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

Are you able to request their balance sheet / income statement?

But I would remain open to long-term rental as an option as this seems like a more stable option in terms of income, again this may be my inexperience talking.However, I have always  been somewhat risk averse and investing in real estate is always a big venture, in my opinion/experience, in terms of capital.