I'd go for the Model 66, for the following reasons:
1. Many, many more accessories (e.g. holsters, speedloaders, grips, etc.) are more easily available for the K-frame than for the N-frame (particularly concealment holsters like IWB designs). It's not that they are not available for the N-frame, but less dealers stock them, and they are made in smaller quantities by manufacturers, which makes getting hold of them problematic sometimes.
2. The K-frame is much easier to carry concealed: smaller, lighter, and a more compact grip frame.
3. The smaller grip frame on the Model 66 will be more "user-friendly" to a wider variety of hand sizes (e.g. your wife, your kids) in an emergency than the larger N-frame.
That said, I still love N-frames, and have several of my own: but I don't often carry them, due to bulk, weight and general concealability issues. If you choose the N-frame, you certainly won't be sorry, but it will be less versatile than the K-frame for everyday use.