I´m personally a bigger believer in decentralization of the governing apparate, so no, I would not be in favor of having a One World Government. Its like OMG, but the filling is turned upside down
In my opinion, the power apparate too centralized is too far detached from problems of ordinary people to truly be able to recognize the real issues, and deal with them.
And also, I was always the paranoid one, so in case the ones at the top were bad ones, there would be almost no way of how to change things. If they were tyrants etc. I already see some people in my government who would crack a hyena smile when getting so much power.
To cut it short, the future of prosperous world, in my opinion, is so decentralized, that it may almost enter the realm of anarchy. That would be a long run thought.
And for that, I´m not a big a of the centralization tendencies (EU, re-emerging russian federation, North American Union, Islamic Khalifat etc...). Its often argued that the coalitions are made for more stability, and mutual help. I just never agreed that help and cooperation should be based upon a signed contract.