Both can create or resolve ambiguities. For my money, the Oxford wins as it resolves more common ambiguities than it creates. Omitting the Oxford seems to me more likely to create ambiguity in more scenarios. So I'll use the Oxford unless it's one of those rare instances where it creates a problem.

As for the double space -- I know, I know. The future left me behind. But old habits die hard. I don't see a day any time soon when I'll be able to train myself to click that space bar only one time.