What to use for bait depends on what time of year. In the spring when the wasp queen first appears she will be feeding on the nectar of flowers, ie, sugar. Later as the nest gets built and the eggs hatch she will be seeking proteins to feed those larva, and as the year winds down the worker wasps will also be seeking proteins to feed the queens that will be seeking to survive the winter.
Most all flies can be attracted to sugar anytime.