Depending on what you would be investing in, and what sort of risk characteristics it has (expected return, time frame, variance of returns, etc.) I would be generally inclined to pay off debt unless the investment offers better risk-adjusted after-tax returns.
For example, if your mortgage has five year remaining and carries interest at an effective annual rate of 5%, and your alternative is a five-year corporate bond with the same effective annual rate of return, you are better off paying off the mortgage because the cash flow you free up from paying off your mortgage is riskless and tax free, whereas the bond issuer could potentially default, and there are taxes to be paid on the interest (if held in a non-registered account).
As long as you have debt, paying it down is a riskless alternative to any investment (unless you actually think you will need the cash for something more immediate).
For example, if your mortgage has five year remaining and carries interest at an effective annual rate of 5%, and your alternative is a five-year corporate bond with the same effective annual rate of return, you are better off paying off the mortgage because the cash flow you free up from paying off your mortgage is riskless and tax free, whereas the bond issuer could potentially default, and there are taxes to be paid on the interest (if held in a non-registered account).
As long as you have debt, paying it down is a riskless alternative to any investment (unless you actually think you will need the cash for something more immediate).
