Your fabricator has dealt with these questions repeatedly. I'd ask him.

is your room contemporary or traditional. That will dictate the style you want. Do you want under counter or drop in? Do you want the whole top to be integrated with the sink or separate?

I recommend drawing up the size of the counter on graph paper and cut up scaled sinks in different sizes and see what looks good to you, and your need for counter space. I did this for my bathroom some years back and it was very helpful for me. Of course you can use a computer program too. Here's what I mean, the sink, tub, and toilet, at the initial stages of this exercise, were all moveable. I just moved things around.

Kohler has a ton of sinks. Look on their web site. Here is a link to rectangle sinks on their web site:

http://www.us.kohler.com/us/browse/bathroom-bathroom-sinks/_/N-2562Z7kZ1z141ts