As a client since the first commercial release I am very happy with Interworx. It is better in every way to cPanel, and with 3.0 things will be even better.
As an admin, one of the best things about Interworx is how fluid its interface is.
I have never liked Plesk as a user or an admin, it has some nice features but over all can’t say I like it.
cPanel is over rated, the only reason potential hosting clients ask for it is its the most recognized brand.
Performance wise, Interworx is the leanest of the top CP’s out there.
Feature wise before the 2.1 releases there was lots missing, but they filled in just about every gap.
Security, as a CP its more secure then cPanel, system security, there are some build on features, but if your serious about managing your server you will go above and beyond anything any CP will give you.
Interworx is very flexability, and with the expanded API that 3.0 brings things just got way better in that department.
“Would you recommend this as long term wise decision?”
Before 2.1, it would have depended on your needs, at this point I would say its the best option out there unless you go custom, but thats completely different.
Sorry if anything is not clear, been working nights and I am tired.