rapidestate has already described 3 different financing methods to buy houses. Please read.
http://bbs.wenxuecity.com/tzlc/1241287.html
My approach is the following:
1. never use HELOC for long term financing! HELOC money is very liquid, that can help you to bid on houses that you like and you don't have to wait for the money. But HELOC rate is an adjustable rate and it will go up and down based on prime rate. In current rate normalization period, we will expect the HELOC rate going up more for the next 2 years.
2. once you get the house, you should look for a way to pay back the HELOC asap since the HELOC adjustable rate will add more unknowns to your house expenses.
To pay back the HELOC, you have several ways. 1. is to convert the HELOC amount to a fixed rate loan by using Home Equity Loan. or 2. if you have a house with more equity than the mortgage, you can refinance the mortgage with cashout option and use the cash to payoff your HELOC.
The bottomline is to max your buying power to acquire more rental properties and at the same time to fix/control your interest rate expenses in your rental business.