Best mortgage options today

[William Allen]

I am new to the forum and am about to buy my third investment property.  My question is about today's best method of getting a mortgage. 

I am looking to get a 30 year conventional mortgage with 20% down.  In the past I have shopped around with brick and mortar banks, internet companies and credit unions I belong to.  However, I was contemplating using zillow or some of the other companies that use multiple lenders to find the best rate.  

What is the best method of finding the lowest rates today from all of your experience?  I know my loan is going to be sold the month after I get it anyway so just looking for the best rate and lowest upfront costs now.  Thank you in advance!

-Bill