I've used them all, plus several not listed here: Tickpick, Tickets For Less, Ticket Boat, Razor Gator, etc. I've only had problems with Seatgeek and Tickets For Less. Seatgeek sold me tickets in a section that didn't exist, but I caught it before the event and filed a claim that took a month to get my money back and I won't use them again. Tickets For Less is a broker in a pool and they sold me tickets that they didn't have and couldn't deliver. They refunded right away, but were huge jerks about it and their guarantee is worthless. I've used them since, but always while holding my nose. I prefer Tickpick and then Stubhub, but will even use ebay if the price is right.
On the fees, it's pretty easy. The fees are either built in or published. A lower price with higher fees is still a lower price, pretty simple stuff.