If you really wanted to, I'd say the shorter mortgage should be paid down first.. 

The transactions are sooooo much easier than conventional mortgages, but the deal has to pencil out at the higher rate and shorter amortization.

@Joe Splitrock, it says no leases shorter than 6 months.

Fannie Mae generally requires lenders to obtain a two-year history of the borrower’s prior earnings as a means of demonstrating the likelihood that the income will continue to be received.However, a person who has a shorter history of self-employment — 12 to 24 months — may be considered, as long as the borrower’s most recent signed federal income tax returns reflect the receipt of such income as the same (or greater) level in a field that provides the same products or services as the current business or in an occupation in which he or she had similar responsibilities to those undertaken in connection with the current business.

Some financing is better for longer term holds and some for shorter. 

Add to that the various "HQ2s" that are coming which implies the major, high paying employers in the area will not be hiring as heavily as they have in the Seattle market, and you create a possibility of lower demand plus higher interest, likely creating stagnant prices in the near future.Therefore, back to my first comment: if it will cash flow on a monthly basis when accounting for management, leasing commissions, repairs and maintenance, Capex, taxes, insurance, loan payments and vacancy, then it won't matter if you see appreciation in the shorter term.  

HELOCs are typically shorter term with an adjustable rate.

This allows us to budget the funds needed to handle possible tenant issues.After we acquire the property we will hand the tenant a form that is really a shorter application where they will fill in their current contact information, employer etc.

The mortgage is a long-term, fixed rate loan charging compounding interest; the HELOC is a shorter-term, variable rate line of credit charging simple interest. 

I had a tenant sign a year lease, and I recently reached out to ask if they intended to stay another year, to which they responded by asking if it would be possible to shorter the lease length to 6 months.