Theater

I have used a couple different companies that I found on the internet - they were all similar in price and service.
I found the cheapest prices by going to the theater ticket office in the AM when it opens and buying tickets for that day/or evening performance.
I have also used the ticket counter (discount tickets) at Leicester Square - but they don't have tickets for all plays that are showing.
Theater in London is wonderful - when I go for a week, I usually see a different play each night.

I generally buy from whichever agent operates the theatre's box office; usually they have the lowest fees. I've bought from various agents over the years and have never had an issue. I always choose to pick up the tickets at the theatre box office.

One website that I like for planning is theatremonkey.com. This site has information that shows which agency operates the box office, the fees that they charge, and seating plans for the theatres with opinions on which seats are best.

Listen to Laura. Theatre monkey is the best site for everything theatre. I have used their site to find tickets for many plays, buying from different vendors, never had a problem. You will have to go to the box office a few minutes before curtain to pick up your tickets at Will Call.

I've always called the theatre to purchase tickets.

Another vote for theatremonkey; their seat reviews are helpful and I've definitely used their directions for finding the theater. We spent a theater week in London several years ago and did a combination of approaches. The TKTS.co.uk website shows what's on sale each day, and I started checking it some weeks in advance to see what shows would be discounted when we were there. We had one or two shows that we knew we wanted to see which were not showing up on TKTS, so I contacted the agent for that theater to order tickets which were mailed to us. [I can't remember if I got that information from Theatremonkey or from the show's website.] And we also just showed up in the morning to buy tickets for that day's performance, when a show wasn't being offered at a discount at TKTS. Note that TKTS also sells full-price tickets. Have a great time!