There are four common protocols for network access of SVN.
http:// has a serious overhead, especially when dealing with thousands of small files. I used svn for a website that had around 50,000 icons, all saved in SVN. With HTTP, it took around 20 minutes to checkout. Once I switched to
svn://, it took less than a minute. This is because with HTTP it's one new HTTP request per file.
http:// however has the following big advantage: it usually goes through firewalls. For example, now that I switched to
svn:// I can no longer access my repository from my university because of their firewall.
Regarding the difference between using SSL/TLS or not, well, it's obvious: data is encrypted; however it's more difficult to set up.