You can usually get a decent hotel at a decent price off hotwire/priceline.

Of the 3 areas, downtown is your best bet. Parking is not a problem. $1.5/hr meter for 2 hours on the street is available near all the hotels. Free after 6 pm.

No nice hotels near the airport.

Glendale is not convenient for most people.

Tip: Don't advertise your area (other than "Milwaukee"). You don't want to tip off local LE to focus on you.