Hello,
Both of them are good products. But most importantly, what kind of user is your friend? I mean, if he/she is a Power User, and likes to tweak the settings of a product, Comodo will suit well to him/her. But if he's/she's not that much of a tech-savvy person, and dont want to deal with popups or do some advanced setups, then go for AVG.
Pros and cons :
Comodo
+Comodo has firewall, and its usage basics is more well-rounded.
-Its not just simple-to-use as AVG, Avast! or Avira etc. Needs more attention, lots of user-decided pop-ups, good for Advanced users.
AVG
+AVG doesnt include a firewall in its Free solution, yet its well-enough to protect a normal user in a daily basis of usage. Good choice for Normal users.
-Some advertisement pop-ups, slightly lower detection rates, yet still acceptable.
Some similar free and good AV options just as AVG : Avast Free, Avira Free, BitDefender Free and the list goes on.. Just test and decide which one suits the best!
Have a good day!