Before answering this question, please notice the following facts:
1, Currently, the mortgage rate is so low that it is like banks giving you free money to make more money on. The average mortgage rate is about 3-5%. The real inflation rate, according to my observation, is about that level. So that is actually money free of interest.
(The government inflation rate is "very carefully" calculated to look good, just like the unemployment rate. Any one who is unemployed for over half a year is not considered unemployed, because the government thinks they are not looking for jobs...)
2, HELOC, as many observed, has a variable rate, and the rate is usually higher than a mortgage. BTW, if you hit AMT, interests cannot be deducted for HELOC and HEL.
3, Making good money in real estate (in fact in every trade) is about leveraging. If you do not leverage, you just turn your active income into passive income, which is OK but can barely get you out of the rat race. Of course, leveraging comes with risk, but you cannot earn money without taking risk.