Until now it has been the cockroach. But I think the ants social structure will make it the most versatile insect in the future. It has been why we the homo sapiens- relatively poorly adapt creatures - are a succesful species.
usually the generalist will surive most evolutionary ordeals...therefore the cockroaches get my vote. about the social structure: i think that the social structure of ants is too structured to be compared to the human social structure. We are more adaptive to our social structure, a generalist even in that, and hence we have more options. Ants are stuck with what they have.
The cockroach is an unevolved barbaric generalist but is almost certain to survive as is. Some variety of the ant, perhaps the fire ant, will almost certainly survive but may change some. They are the most highly evolved organisms on your list. They would not do well in a mass extinction, The mosquito is likly to do reasonably well as long as large mammals do. It is very specialized and if there is a big change in either the enviroment or the mammals they subsist on they will die. The housefly species is reliant on lots of humidity and warm temperatres for the incubation of its larvae and climate change could spell doom for it. They also are constantly developing new specialized forms to make do with new food sources.
