Do you prefer the Perforator or the Infiltrator, and why? Not sure which I should keep/use.

I prefer the Perforator.
With my previous just-died character, she had a Small Guns of 90. Having not yet gone to Point Lookout for the game-killing perk, Perforator does about 40 damage as opposed to the Infiltrator which only gives 35.
In all my time playing FO3, the Perforator always has a higher damage than the other. What's awesome is giving a follower the Chinese Sneak Suit, and the Infiltrator. Keep the Perforator for yourself.

The Perforator is a higher damage, unique variant of the Infiltrator.

Guess which one is better.

Another advantage of the Perforator is that you can repair it with common old assault rifles. The Infiltrator needs either another Infiltrator or an NPC for repairs.

Thanks everyone