Does the free version 3 firewall and D+ protect as well as 3.5? I have an AV that I am happy with.
Of course there have been improvements in Comodo Firewall 3.5 and therefore it has better protection than CFP 3.0.
Comodo Internet Security is basically a package which contains Comodo Antivirus and Comodo Firewall but a user is not forced to install both of them. You may choose either to install Firewall or Antivirus separately or both of them as a whole package or should I say security suite ;).
Yep, As fOrTy_7 said, use v3.5 for the fixes & improvements. 
Josh