Lisa...I think in your kitchen you could go either way. Regardless of where your (main) sink ends up, it will still be close to the cooktop & you will have room to prep b/w them. If the sink moves to the refrigerator wall, you will have even more prep space b/w them. While a prep sink would be nice, I don't think it's a necessity to make your kitchen work. Yes, it would add an additional prep area for you at the island (b/c there will be a water source) and, possibly, reduce some zone crossing, depending on the location. Right now, to get to the refrigerator from the cooktop you have to either cross the Cleanup Zone or go around the island. How many people will be using your kitchen at once? Will they all be prepping/cooking or will there be a mix of prepping/cooking/cleaning up? If cleaning up is in the mix, then the zone crossing could become an issue, especially when the DW is open. As to location, I like Elizpiz's setup best, but I can see where it would definitely reduce available counter space. If you put it on the left side across from the cooktop, it would be readily available from the cooktop as well as the "outside" part of the island for prepping there while someone else is cleaning up on the "inside" as well as be available for outsiders for a drink of water, etc. However, it will reduce that 42-1/4" to approx approx 24" of workspace directly across from your cooktop; but, as I mentioned b/f, you will still have add'l room on the wall run. If you put it on the refrigerator end, I think you're right in your assessment...I find that I use the counters across from both my refrigerator & ovens much more than the counter next to them...both for removing things from them as well as staging things to put in them. (I have approx 32" b/w the Ref & DR peninsula end and approx 44" b/w the ovens & the end of the "mini peninsula". Both have landing space right next to them as well.) We do have a prep sink, but in our kitchen it was a necessity to make it work. Our cooktop & sink are opposite each other, separated by approx 6'6" of aisle...the main aisle through the kitchen. By adding a prep sink on the cooktop wall, we were able to separate the Cleanup Zone from the Prep & Cooking Zones as well as protect both zones from kitchen traffic (inside a "U" w/short legs but long base). During the week, there are usually two of us in the kitchen...one prepping/cooking (me) and one cleaning up (DH) with an occasional child helping make veggies. On the weekend, there are sometimes all four of us working in the kitchen! When baking (usually a marathon!), there are usually two or three of us. (I seem to bake in spurts...when I bake, I seem to go all out!)

Our prep sink is 15-3/4" x 15-3/4" x 7-1/2" (plus 1-1/8" granite depth = 8-5/8" total depth). It's big enough to work in and big enough to fit all my colanders and all my pots for filling, although I find filling the pots on the counter much easier. When we were shopping for a sink, our KD told us any sink less then 12" in each direction would be useless as a prep sink...now that I have my sink & have worked with it, I have to agree. Actually, I might even say any that's not at least 15" in each direction would be useless b/c I don't think a sink any smaller than mine would be as useful for prepping. You have to have room for your hands + whatever you're working with inside the sink. Our sink is in a 36" corner sink base. In a "regular" sink base, a sink base at least 17" wide would be fine. Here's mine...

Mine is approx 18 x 16" (outside measurements). It works pretty well. I wouldn't want smaller, as it's great for emptying pots into my colanders, and working on veggies...having plenty of room for a good batch and to deal with them without bashing my knuckles on the sides of the sink. In my 'dream kitchen' I would probably have a 24" or even 30" sink, so I could also hand wash my cast iron pots and skillets.

My island is about 3x7 and my prep sink is 15+x15+. With a larger island, I'd go to at least the 17x17. I was thinking possibly 21 or 24 inches. I wouldn't go larger than that, but having a little more room gives you more flexibility. A larger space makes it easier to dump out hot water without worrying about a splash problem. It also makes it possible for more than one prepping task to be handles at the same time. For any size space, I would be concerned that the 14x17, if it has much of a radius at the bottom, you might not be able to set large pots or such flat on the bottom if you needed to. My prep sink is in a 30 base with a disposal and there is plenty of room for our pet foods and supplies in the cabinet below -- with the dry dog food in a container that would be a decent size trash container if you don't 'put a pullout next to the sink base.