As stated by Tailseh, it depends on your level of traffic. If its a constant level of bandwidth being used, say in excess of 3Mbps concurrently most of the time, an unmetered line is a better as you won't pay any bandwidth overage fees.
However, if your traffic tends to be spikey, as in you get the odd burst of traffic every now and again over 10Mbps, but for the most parts its nowhere near this, then you will be better on a metered lin. Of course, this depends on whether you can get a bandwidth deal to suit your requirement. If you are going for a metered server, its best to get a 100Mbps port rather then a 10Mbps for most applications.
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