SubmitHub isn't for everybody. For starters, you need to have tough skin. Even the most-successful submissions still get rejected by most of the outlets they send to.
There's a *lot* of music out there, and not everyone will like everything. Curators in particular are a very picky bunch.
If you've got a well-produced song that you think is ready for the world to hear, curators are often a great way to get a better understanding of the audience that will (and won't) like your music.
If you have an unfinished track or are looking for a second opinion, sending to the curators probably isn't a great idea, as most of them are looking for finished products. You might want to try out Hot or Not, where other artists can rate your songs.