Specifically, TCP doesn't lose any packets, and the packets are ordered. With UDP, packets may not arrive in the order they were sent and they may never arrive at all. So you need to write your own system to handle lost or unordered packets if you plan to use UDP.
The current wisdom seems to be to use TCP for important data ( like selling an item ) and then UDP for less vital things ( like a regular position update. )
The current wisdom seems to be to use TCP for important data ( like selling an item ) and then UDP for less vital things ( like a regular position update. )