Depends on the style I'm going for. For traditional I tend to use oval sinks. For modern or transitional, rectangular. I prefer undermount versions; they look cleaner.

It depends on the room[ bathroom, kitchen, bar , laundry ] , function and design style.

Since I do 90% contemporary design i like rectangular or square depending on the vanity

For personal use, rectangular. I prefer the full usable width of the bowl being close to me instead of curving away from me.