For those who're asking "Should I use TCP or UDP for our online game?" this paper should answer that question
Our analysis indicates that TCP is unwieldy and inappropriate for MMORPGs. This is due to four distinctive characteristics of MMORPG traffic: 1) tiny packets, 2) low packet rate, 3) application-limited traffic generation, and 4) bi-directional traffic...Furthermore, TCP is overkill, as not every game packet needs to be transmitted in a reliably and orderly manner.
The suggested approach is to use a hybrid approach of "using UDP, RTP, or DCCP as a basis for unreliable transmission, and using SCTP and RDP as a basis for reliable transmission."