Which AV Solution to deploy

I have a small office setup, with 2 server running Linux (one is also running mail server) and 5 clients running windows (all version).

I’d like to know which Antivirus product can I implement for both server & linux, and hopefully 1 that has automatic update & push like symantec. Was told Sophos could not do the auto push to clients. How about NAI or Trend Micro? Any suggestion ?