These Heroes are (1) Strong when played well & (2) do not rely on their team too much to be effective = There are really good chances of getting yourself a win. Some of these Heroes are also the ones that are apparently effective at their job when played by almost any player (Raynor, Imperius, Jaina)
It is usually good to keep an eye on these Heroes in the course of the quickmatch.
Although there isn't any real Meta in quickmatch, these heroes tend to be the ones that many seem to be especially good. Many players queue with these comfort picks to get a win, because they know they're strong with them. I'll give a wild 60% of the time these players on these heroes tend to know what they're doing.
The reason why I call this tier the "Party Picks" it's because it really depends on the team's cooperation. Many heroes here aren't the strongest, even with a knowledgeable player, and some need the change of playstyle of the entire team to be strong. There are occasions when the carelessness of the friendly team is less harmful than that of the opposing, and will help get a win.
These are Heroes that tend to be played badly in quickmatches. Either from the skill floor being too high, being too reliant on team/self/fight setup, or everything at once. They're also easily exploitable and some just have that mind & vision tunneling factor that really makes the player overconfident and overextend. I falsely blame funny moments for that "overextending" problem.
I don't know why that is, but Cho'Gal and Stitches seem to have a problem in cooperation... usually by their own team. They also have really easily exploitable weaknesses in the quickmatch realm, such as team split focus.