Stick with Ticketmaster...
We bought three tickets to see muse at Wembley Stadium. All great... About 2-3 weeks before the concert, our tickets still haven't arrived, so we looked up this worldwideticketstore.com. Sure enough, there were complains and rants about this company. Luckily we managed to get a refund from our credit card company and we had also accidently bought another set of tickets off ticketmaster... We were lucky, but other may not be.
Stick to the sites you know, even if other sites are offering them cheaper. We will only use ticketmaster and it has always been reliable. AVOID!