When I had a mortgage I concentrated paying it off. I don't like debt. Could I have made more in the market? Perhaps. But I have been debt free for the second time, this time around for about 10 years. Cash flow is insane, and I have no money worries. In fact, just yesterday I was checking my bank account and noticed the balance dropped significantly. I inadvertently paid 10x more than was due. It is a mere inconvenience that Chase is holding a ton of cash for the next 4 to 6 months (called Chase and don't want a big check sent though the mail) as credit for future credit card bills (spread across 3 cards for my wife and I). In the days when I had a mortgage, even without paying it down, I likely would not have had the cash on hand for a mistake like that. Plus, over the yearsthings like new flooring, appliances, doors for the house, etc, are easily paid out of pocket.

So my preference is debt first. If you do invest and are hesitant due to "high" equity prices, pick a fun that is a mix of stocks and bonds. Last year I started a new house fund, which I use VSMGX for stability.