This article is from the Theatre FAQ, by aku@leland.Stanford.EDU (Andrew Chia-Tso Ku) with numerous contributions by others.
Many people prefer buying tickets in person at the box office: there
are no service charges; you can refer to a floor plan in front of you;
and you are handed the tickets on the spot. The major drawback, of
course, is that you have to be in New York to buy tickets this way, or
at least have a friend do the schlepping around for you. If you
are visiting from out of town, you can always gamble and wait until
you arrive in NY to do your ticket shopping. If you only need singles
and don't go after the monster smashes (PHANTOM, SUNSET, SHOW BOAT)
you may be pleasantly surprised by the (full price) seats you
can get a day or two before the performance.
The manner in which ticket inventories are maintained has always been
shrouded in secrecy, but some have felt that the quality of seats sold
via the telephone agencies weren't as good as those sold in person.
That perception may have been largely shaped by the refusal of the
phone agencies, in the past, to reveal seat location, thereby allowing
them to stick phone purchasers with poorer seats that would have been
refused by an in-person ticketbuyer. Now with both Broadway ticket
agencies (Telecharge and Ticketmaster) giving out seat locations over
the phone, this perceived disparity may no longer have any basis.