The Milwaukee Airport (MKE) is a very easy mid-sized airport. There are non-stop flights to/from most major U.S. hub cities. This includes non-stop flights from Atlanta, Boston, Chicago, Dallas, Denver, Detroit, Houston, Las Vegas, Miami, Minneapolis, Nashville, New York City, Orlando, Philadelphia, Phoenix, Salt Lake City, San Diego, Seattle, Washington, and many others.
The Milwaukee Airport is a 15 minute Uber ride away from Downtown Milwaukee in what is almost always easy traffic.
If there is not a good non-stop route into Milwaukee Airport, you may want to consider flying into Chicago O'Hare (ORD) instead. Sedan service never takes more than 1h15m curb-to-curb between Downtown Milwaukee and the Chicago O'Hare (ORD) ticket counter. I personally fly in/out of both MKE and ORD depending on where I am going, my risk tolerance for missed connections, flight prices, and whether I am flying internationally.
More details at: https://agilecarpentry.com/clp/mke/plane/