It depends on factors such as material availability, plant preference and access location.
Crosses with two blind flanges allow cleaning in two directions, while a tee (with 1 blind flange) will allow cleaning in only one direction. Flanged 90 degree elbows allow cleaning in two directions, but are more difficult to unblolt from the piping compared to a blind flange. (depending on the piping layout, you might require temporary supports).
Coke will build up inside of the pipe. I have seen 1-1/2 inch buildup inside the transfer line.