SVN in Eclipse is spread into two camps. The SVN people have developed a plugin called Subclipse. The Eclipse people have a plugin called Subversive. Broadly speaking they both do the same things. What are the advantages and disadvantages of each?
Both are very similar but Subversive is the "eclipse svn provider". I primarily use Subversive because of a few convenient features:
Grouping of history
When I'm browsing the history of a branch instead of just seeing a bunch of rows for every commit it can group commits by today, week, etc.
Mapping of trunk, branches, and tags
Subversive assumes the default svn layout: trunk, branches, tags (which you can change), so whenever you want to tag or branch it is one click and you provide the name of the tag or branch.
Like I said these are minor differences that I just find convenient. Both work great with mylyn, but overall there really isn't a whole lot of differences with these two extensions.
Merging with Subversive is a pain though (haven't tried Subclipse), I've never been able to successfully merge. The preview of the merge is great but it would never complete the merge or it will take way to long. Most of the time I complete merging through the command line without any issues.