I've been trialing ShareTool (there's a generous 15min connection limit unregistered) and from what I can tell it just works.

I connect from home on ADSL2+ straight through my works firewall to my desktop Mac. I can only comment on my reasonably high speed connection, but the performance is great in screen sharing mode. I love how I see all the shared connections on my work machine as well, as if I was sitting at the computer. Now there are no boundaries between work and home (is that a good thing? ;)

As soon as these guys release an iPhone companion, Im there!

PS. I cant justify 5 stars because - to be fair - I haven't tried the competition to the same extent. I like the natural mac-like interface and ease of use so much.