Once you’ve decided that getting some expert feedback on your song is a good idea you then need to decide who is the right person to ask and how to access them.
As a rule of thumb, you should try to seek out the services of someone who has been successful in the market with similar music to your own. I would suggest going with a songwriter or a producer. My next choice would be an accomplished A&R person. These are the three kinds of people who have been successful because they write, record or find the best songs. So, they certainly know one when they hear one or are in the business of polishing good songs to make them great.
I find that crowd sourcing (playing the music for a focus group of music fans) and asking your non-songwriting friends and family is not the best idea. Fans tend to hear good production and can imagine hearing your song on the radio but they aren’t objective when it comes to whether or not the song is compelling. Friends and family are invested (at least emotionally) in you and they cannot be objective.
Furthermore, keep in mind that songs catch fire in the market by a lot of people hearing the song in situations when they aren’t actively listening (while shopping, driving, during ads, in the background at restaurants etc). You can’t easily re-create those situations but professionals who have been successful time and time again really know what a hit song is all about. Of course, my company is in the business of enabling artists to interact directly with music industry professionals so I’d be remiss not to point you here for some of the best in the business.