The problem with any of these sites is that the third parties selling the tickets, are, for the most part, all listing their tickets on multiple sites at once.
Accordingly, there are occasions when the independent brokers sell their tickets on multiple sites at once, meaning that somebody is not going to get those tickets.
TickPick, StubHub, etc., can't control that. But, they can help you to identify another seller to purchase other tickets from, and they can, if they want, "ding" the seller who didn't send you the tickets.
But, keep in mind, these sites DO NOT send you the tickets themselves. They are intermediaries, who manage a web-site.
As the OP mentioned, TickPick doesn't charge additional fees at the end. So, it's at least nice to know exactly what you are going to pay before you get add-ons at the last minute.
Other than that, I'm not sure that any one of these sites is significantly better than other, but people's perceptions will be framed by their own experience.
My experiences with TickPick have all been good; accordingly, I have no reason to complain.