3 cross. at 4 on such a small wheel (if nothing else) you get into some weird angles and have the spokes put pressure on the hub flanges, sometimes cutting into them.
I use a 4 cross under the 4th spoke lacing for my 48 hub rim/hub. Works perfectly.
I was gonna use a 4 cross under the third, over the 4th lacing but decided it was too much of a hassle to bend the spokes enough to get it under the 3rd.