I have been trying a combination of roundcube and owncloud (version 8.2) instead of SOGo or Webtop for the last 2 months.
This combination has some useful features that is missing from either SoGo or Webtop -
Main feature has to be the ability of using both local and remote file servers / cloud access (ftp samba, Amazon EC, Google etc.), and being able to connect via Webdavs.
Owncloud also has both Caldav and Cardav access (the web-gui for the calendar and contacts are both ugly and crap to use – but using the OC extensions: calendar+ and contacts+ vastly improves the UI)
There is a OC extension to wrap Roundcube within Owncloud, and both can authenticate using ldap and imap.
I have also got to agree with @robb, I don’t like java apps and would prefer php based UI) and rather would stick with SOGo.