If you are asking about SVN server, I tried many and found that the two very best are:
1) SVN Server for Linux; 2) for Windows, Visual SVN server is by far the best.
It also depends on this: is your team distributed, or it is in one LAN. If the team is distributed, I would recommend dedicated development Linux server and HTTPS (you will also need a certificate, at least self-signed).
As the the client SVN, I think this is a matter of decision of every individual developers. I, for example, hate the idea of Visual Studio plug-in. First, it's too intrusive for me, and, more importantly, what to do with non-VS development? To me, the ideal solution is TortoiseSVN. Seriously, you should only recommend developers something, but never enforce any particular client. Developers can decide by themselves.
As far as pricing and license are concerned:
Here is the idea: I advice to use only the server authentication, not Windows. We usually worked on a local domain without passwords, to make it less annoying. Why not? Nobody from outside worlds cannot access it anyway, and all the moves are recorded.
If you use passwords, the are not stored anywhere, like with in a decent system (hash functions are stored, finding out passwords is cryptographically infeasible
). So, even in distributed international team, we used SVN authentication, via HTTPS, for safety.
All other Enterprise features are absolutely not needed, simply because people playing the role of administrators can access the server's host locally.
In other words, if your team works in the same LAN or same domain, free-of-charge "Standard Edition" is perfectly suitable. And when and if you grow out of these settings, you can later easily grab your code base (this is nothing more then a directory with files, in SVN format) and copy it into any other host and configure with any other server, including some which are non-SVN. No vendor lock-in, really.