It isn't the better system the earlier you can tell...it's the developement of the baby and when it occurs. The earliest you can tell is 14 weeks because this is when the scrotum actually drops for a boy and when the vagina has developed enough to determine the 3 white lines. Some boys who are late developers don't drop their scrotum until later than 14 weeks...if this is the case the gender is often mistaken for a girl when it's actually a boy. The only way to know for sure if it's a girl is 3 very pronounced three white lines showing the lips of the vagina. If there is just an absence of a penis you cannot know for sure and you have to wait another week or so to be sure of the sex.

4D ultrasounds aren't really of any use until about 23-25 weeks, at the earliest.

Your best bet, is to wait until 20 weeks for a 2D ultrasound to determine the sex.

a 4d ultrasound isnt good until your like 24 weeks and on. its kinda pointless any sooner. even thats sometimes too soon. if your tech is good they should have no problem getting the gender!!!!!!!!! they kno all the tricks to get the baby to move.