Pay off Morgage or buy more Rentals

[Douglas Graves]

Hope this question is where it supposed to be.

I have 8 propertys, 5 of which have loans.

All total they clear about $7000 a month.

I have a small side business and my wife is a killer realtor earning us an additional $150k.

Over the next 2-3 years I'm expecting to have up to 300k+  in available cash.

My question is, now that we've established our rental business. Should we go with the sure thing and simply pay off the Morgages (all are about $125k at 5% with 25 years to go) 

Or 

Start investing in stocks (most likely Vanguard total stock market fund) and other funds?

p.s. I'm not wanting to buy more rentals in this market. 

Thanks For Any Input,

Doug