I too tried clients and in roughly the same order. My findings:

LimeWire:
. nice interface, intuitive to use.
. unacceptable CPU usage -- roughly 20% of my PIII/600.
. unacceptable bandwidth usage. though set to limit its upload bandwidth to roughly 56k speeds it chewed through over 200 kbps as measured by the router through mrtg. looks like mostly query-related traffic.
. grew in RAM to around 20M
. written in JAVA

BearShare:
. comes shipped with too much extra stuff -- streaming advertisements, an alternate-TLD plugin that excludes .web, some undocumented wizard, etc.
. much better on the usage. 5%, while sharing around 700 files and connected to three hosts.
. runs around 30kbps (self-reported) just for the queries.
. per-connection upload figures are really bouncy. not averaged over even the past few seconds.
. using 17M ram.

Gnotella:
. after reading the thread on CPU usage i avoided it entirely.


Until a client is devised that can better manage its utilization of the physical network, this is not a service I can leave running 24/7.