Again, it's your Mac and your usage habits (not mine) which should set the criteria. In my case (scanning the occasional app), Clam is my cup of tea.
I opened up Sophos with Pacifist for a look/see (some time after posting the link here) and espied a ton of stuff which didn't interest me. Sophos is around 3-times as massive as Clam... but you're right: it seems to have more features (such as hooking into the browser to analyze downloaded items or something?).
I posted that Sophos link strictly as a relevant "news" item... not as an endorsement or recommendation. [it's brand new AFAIK, and currently i'm not inclined to even install it.]
