Nails 4 U is by far my favorite place to get my nails done in Madison. It's worth noting that they are temporarily in an office building while their new salon is being built next door, but they should be back in the regular salon in Summer 2017. In the meantime the temporary space is totally fine, just a bit awkward to get to the first time.
Regarding the service, this salon is tops. They are appointment only, and unlike other salons, they honor your appointment time so you can be assured you'll get in and out in your timeframe. I found their regular manicures last up to a week without chipping, and the shellac is great--I did not experience the same weakening of my nails as I did with other shellac manicures.
The technicians are friendly and professional and seem to know their regulars well. I'd highly recommend Nails 4 U!