Given
ClamXAV is freeware, I would not consider that as a major, or even minor, selling point. I can't comment on the bootable emergency drive as I have not seen it work. For what it is worth I have used ClamXAV for years and it has, from time to time, detected several Window viruses in incoming email attachments. It is very unobtrusive and it works, the unobtrusive part is more than most anti-virus utilities can claim.
Cocktail was one of the very earliest GUI front ends for the built in BSD Unix commands line utilities. Today it has lots of competition and each has its own set of unique features as well as duplicating a host of features of all the others and all of them are dependent on command line features in the BSD Unix kernel that undergirds OS X. Among the numerous other utilities that will clean the various cache files are
Cocktail,
OnyX, and
TinkerTool System 2. My personal choice for cache cleaning is TinkerTool System. Not that it is necessarily any better but in my experience it has the most flexibility in choosing which caches to delete.
In the long run, given the plethora of options and multitude of various features offered by the various tools, if you are going to choose only one, pick the one you like and has the specific functionalities you use most often. I have and use several from time to time based on what my needs are at the moment.