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Top page is perhaps the most accessed page, so if that's the news page, I'd recommend some cache on it - Depending on the need for fast updates.
My own site has updates with some days intervals, so a 5-hour or 1-day cache is plenty for me.
Other modules, well - assess each of them and judge, how time-critical they are. Forums are usually best off without cache, but others are not updated that often...