There is TortoiseHG

Truly spoken. I have 3 gigs of client/server bean spaghetti that used to take 40 minutes to checkout, and 5 minutes to run an svn status on. With mercurial, it's more like 14 minutes and 50 seconds. Branches are easy, tags are easy, merges are easy. Haven't found anything I don't like yet.

we are working successfully the last 3 years with Subversion (including successful replication and backup), the last half year additionally with the integration of Hudson. For the next project I would try Mercurial, but I'm wondering if there is an import for Subversion repositories, including history, for our grown code base? On a quick research I didn't found anything on this topic.

if it had an equivalent of TortoiseSVN/TortoiseCVS for me. I've been holding off because there is no Windows x64 version of TortioiseHg.

As a former Subversion user, I really am sorry to everyone who is continuing to use this crappy tool because you know not where to find the truth. Well my friends, the "truth" in the case of a great cross-platform SCM is Mercurial. Subversion is decent, but for Java development is sucks. Why? Because Subversion can't handle merging files when you do a move (actually implemented as a copy + delete in svn). So when you use your IDE to do refactorings, and you rename packages (directories), subversion freaks out and looses history and basically ruins your life for the fun of it. Mercurial on the other hand tracks directory/package renames just fine. Not only that, but Mercurial is a distributed SCM, so you always have all of the history with you on your local box. Mercurial is about 5 times faster than svn (I'm serious), and is much more efficient. Mercurial (like Git) uses SHA1 hashes to track changesets so distributed work can get merged together easily. Also, notice that Netbeans has great Mercurial support. Just too many features to list. In short, Mercurial rocks. Subversion is seriously a waste of your time. Friends don't let friends use subversion (when they could be using Hg)

I have never found a SCM system that I enjoy using so "favourite" is not a word I would use in this context. Note that in principal I like SCM, it is just the available implementations that stink.

Perforce, once yuo get used to it, is very useful.

Though I don't have a firm favourite, Subversion is my preferred. However, there is one that I really dislike... Perforce. It's confusing, expensive and not fit for purpose. I've spent many hours (and several broken builds) trying to master it and I'm still no closer. And the only justification I get from the advocates of it is that it is fast... well, you can keep it and I'll just wait that extra 5 seconds thanks!

We use Perforce at work and it rapidly became my favorite due to its ability to quickly and easily move atomic groups of changes between branches. It also integrates extremely well with IntelliJ, our IDE of choice.

We have been using CVSNT here at work since transitioning away from ClearCaseLT about two or three years ago. Since I haven't used any of the others I can't legitimately pick a favorite. but... The cross-platform nature and general buzz surrounding hg is piquing my curiosity.