Right now, I'm using
SmartSVN.
It comes in Windows, MacOS X, and *nix versions. I'm also using its sister
product, SmartCVS, for the SF CVS repository.
I dunno about other platforms, but as far as MacOS X is concerned this
is the most functional out-of-the-box package there is. I tried multitudes
of different GUI versions (frontends or not) of the SVN clients and either
I need some sort of authentication module from 3rd party (can't do this
SVN+SSH on its own) whose website seem to have disappeared, or I
need a commercial IDE to have it run on, or the thing just fails to work
as I wanted. SmartSVN at least worked right from the start, and well,
it's got a weird problem with saving its own settings (I think I found a
workaround, thankfully) and committing across multiple folders sometimes,
but other than that, it 'just works'. I'm sure these problems should be
fixed once it hits official 1.0 release (started using it in beta EAP8, now
currently at 1.0-RC3).
Oh, and SmartCVS was completely trouble-free for me. That thing's
version 4.0.5 or something, so I guess that's not a surprise.