If you are solo queuing it's almost always best to go for a hero that works regardless of how cooperative your team is. Heroes that can shift roles easily. Axe is probably my favorite hero for solo queuing because he can fit in any role except for hard carry and lane support, and is one of the best early gankers in the game.
Regardless, heroes like Juggernaut, Morphling, Axe, Abaddon, Silencer, etc, who can be in any lane and be relevant regardless of how the game is going, are the best picks for soloing.