T568A is default, T568B is optional.
You can find as many opinions on this as there are people willing to ofer them. We know the origins of 568B. My opinion is that A was implemented in the days when combo data/voice wiring was punched down on 66 cross connect blocks in order to maintain the pair 1/pair 2 order on the block. Since everything is now on patch panels it makes no difference. Pick a standard and stick to it. B is most common in this country.
-Hal
