I've never used Vivid or TickPick, but I have used StubHub on numerous occasions and like Bart, never had a problem. I just bought Keith Urban tickets for the summer through StubHub, as an Xmas present, but usually I'm using StubHub literally moments before a show. I bought third row stage right for the Maiden LOTB tour from the parking lot, and I bought fourth row center for the Sabbath The End tour from the off ramp for Great Woods. In both cases it was flawless, and in fact, I moved up for Sabbath to the second row by noting that two seats in front of me never sold by showtime (StubHub can be a resource for that as well).
I will probably repeat that for Maiden in the fall, when they come to Worcester.