uTorrent can be set up to be MOST disk friendly I guess by tweaking its cache settings. This much of tweaking is not allowed by any other client that I know of.
I can set the cache to 1024 MB, I can set it to write only when a piece is complete, I can set it to retain all the disk reads in the cache so that subsequent reads will happen from RAM than disk (until the cache is full at least)
As I run my client only when I am not actively using the computer for anything else and my PC has 3 GB RAM, I have been happy with it.
I will try any other client only if it has this feature.
I really liked Azureus / Vuze but being based on Java its cache is limited to 256 MB
A bittorrent client that is lightweight but still feature packed is welcome. Hope baretorrent becomes one.
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EDIT:
I am downloading it as of now. For a "bare"torrent, it is considerably anything other than that at 14.44 MB!!!