You basically have to deal with Symantec, a giant in endpoint computer security (like Microsoft is in computer operating systems), offering a product that has seen constant improvement and user support, boasting powerful and tested securtity components, especially SONAR (Symantec's proprietary behavior blocking technology implemented in Norton Internet Security).
As far as F-Secure Internet Security is concerned, you may have noticed that it leases the signature engine and database from BitDefender, so the effectiveness of its signature-based detection depends on a 3rd party provider for that technology (this might be questionable to some, however BitDefender has rather high detection rates). Also, F-Secure utilizes native Windows Firewall modules in order to provide network protection (while this is perfectly fine, one would expect to pay a bit less for a component which essentially provides the same core functionality of an already built-in Windows component). The strongest and most interesting component of this product would be DeepGuard, F-Secure's behavior blocker, which has proven its effectiveness, at least in some tests conducted by AV testing organizations (however unreliable those organizations might supposedly be, one has to acknowledge the fact that they did reward F-Secure with security awards due to the overall effectiveness performance of DeepGuard).
I would go with Norton Internet Security, but that only my personal opinion.
In the end, however, I believe that the choice rests on the user's shoulders, as there seems to be no fine line to distinguish the overall effectiveness and appeal of one security package from the other.
