Version 0.3.1 Stable > 3/5
It's best of the rest, but still further improvements are needed. In Belgium and the Netherlands a lot of webhosting companies use DirectAdmin as their control panel, and RoundCube is often pre-installed on their servers, which is great for inexperienced users who need webmail. Of course they only install the stable versions, without any plugins or patches ...
Further improvements are needed before I really could recommend 100% RC to (all) inexperienced users. For example the option of top-posting in a reply, which is really highly needed imho. I have seen some reply-emails from friends, whom I recommended using RC, and the combination of bottom-postings (RC) and top-postings (Outlook) in one and the same reply-email is very confusing and gives a very unprofessional impression.
I hope version 0.4 stable is released soon, which resolves issues like top-posting, and then RC really rocks !