This is YOUR kitchen. No police will come for you if you mix and match.

Look at your budget first. Then look at your usage of the prep sink. How durable should it be? How functional for my stated purposes? How ergonomic? Will I actually use it? How likely that matching sinks will matter to observers? What is my motive in matching--is this a place that is a showplace to be displayed to strangers?

In my own life, a most important question would have been, "What else can I do with the difference in money? Do I really want this amount added to my loan?" Another important question would have been, "Is it big enough?"

I agree with Florantha. Fit the sink to your needs. It doesn't have to match.

I want granite sinks. I was planning on using Blancos for both the cleanup and prep. I then decided that I didn't have the space for the huge, supersingle Blanco I wanted for the cleanup. Blanco didn't have one a smaller one that was big enough in a shape I liked so I decided to use Elkay for the cleanup. Sinks will be different for me! But you could argue that they aren't really that different because they are both granite, and the materials are extremely close in color and finish.

I ordered a Blanco Silgranit sink in Anthracite for my main sink and a round copper sink for my island. I don't have them installed yet, but am excited to have the contrast. I also ordered a Delta pull down faucet in stainless for the main sink but wanted something with a lower profile for my island so went with a completely different style and color. I really don't think anyone that comes into my kitchen will notice the differences. I think you should go with what pleases you. After all you have to look at it each day. Just my thoughts.
Julie

I didn't match mine. I have a stainless steel farmhouse Kraus Main sink and a Ticor undermount prep sink. I think no one will notice.

Mine are both stainless, but my main sink is KWC and the prep sink is Blanco. I considered a white farmhouse sink, and the prep sink still would have been stainless. I sure wouldn't feel obligated to match brands, but you might find that different brands will have a slightly different finish (the degree of brushed or shiny, polished finish). Most are brushed to some degree -- a few are more polished and mirror-like. If they are both under-mounted, most folks would never notice unless they are very different -- and then they probably still wouldn't care. But if you are the one in the group who could see nothing else --- well, you probably wouldn't be asking.

I have Rohl Allia white undermount for main sink. Needed a special size for my prep sink, so went with white Kohler undermount there. With the stainless grates in each, no one notices. It would be hard for me to tell, if I didn't know!

Thanks so much everyone! I realize that there is no "kitchen police" :) but I just wanted to make sure that I wasn't missing something because now that I'm shopping online and see more affordable options I'm questioning what the plumbing supply vendor had said - such as that I had to have a Franke sink to match. Thanks!