If someone was thinking about buying a second home and keeping the first (living in one and both producing rental income), as a way to invest so there's money in the future for retirement, is it better to do a home equity loan, HELOC, or cash-out refi?

If they were thinking ahead and not moving forward with buying the second property until a year later, which would be a better option to take now for helping to purchase the second home a year later?

Thanks!