Seetickets is my favourite site to use, I have never had any problems and find Ticketmaster makes actually buying and paying for the tickets quite stressful. With Seetickets you just select and pay, on Ticketmaster you have to fill in multiple pages each with a time limit! Also (although Ticketmaster may do this anyway) I get regular emails from See about the whereabouts of my tickets. I had absolutely no problems using them this morning to get my Manchester tickets so I'm chuffed to bits
Sorry to hear about anyone who is having issues.