If your dealing with volunteer choirs, you'll probably be dealing with quite an eccentric mix. My choir always had loads of ladies but it was almost impossible to get enough tenors. (There were even times when we had altos singing tenor--SAAB). If you're writing for very amateur groups, you might want to stick with SAB, but SATB is pretty much the standard. If you want more parts, split the sops and altos, but I wouldn't split the tenors or basses unless you know you'll have the men to sing it. Also, if you're unsure of your performers I'd avoid extremes of the ranges. Not all basses can get those low ds or even fs, and amateur sops won't be very happy spending too much time above the staff.