Never actually owned a Guardian, but here's my take on the subject for what it's worth...
I was about ready to purchase a Guardian .380 about a year and a half ago. That's when I first made the Pocket Semi-Auto Comparison chart to help me in my search.
http://www.mouseguns.com/PocketAutoComparison.pdf
http://www.mouseguns.com/PocketAutoComparison.jpg
At that time the P-3ATs were still very iffy NIB, and being new to gun ownership I didn't want to have to learn how to fix a gun in addition to all the other stuff I was trying to learn.
I didn't want to spend more money than I had to either, that's why I liked the P-3AT. The con on the P-3AT was it wasn't reliable, and the cons on the Guardian were it cost a lot more and it was heavy.
The Guardian at the time was more reliable NIB, that's why I liked the Guardian.
I was ready to plunk my money down on the Guardian when providence intervened, Kel-Tec fixed the ramp problem and fixed the extractor problem at about the same time. The newest SG P-3ATs were now very reliable. And ArmaLaser came out with a laser for the P-3AT. That turned the tide, I got my P-3AT. One of the best buying decisions I ever made.
Today, I believe they compare like this:
Reliability = (a tie).
Ammo options = (a tie).
Number of rounds = (a tie).
Size = Guardian wins slightly in length - P-3AT wins slightly in width. = (a tie).
Weight = (P-3AT wins handily).
Trigger Pull = (P-3AT wins handily)
Cost = (P-3AT wins handily).
Appearance = (this is subjective, but I think the Guardian looks nicer).
Factory Options = (Guardian wins handily).
Laser sight option = (P-3AT wins handily).
Warranty = (a tie).
--------------------------
Ties = 5
Guardian wins = 2
P-3AT wins = 4
Bottom line…
If you want a pretty gun that you can have factory customized and price and weight are not big issues then it's the Guardian.
If you want a light gun that costs little, looks is not high on the priority list, and you can add a laser then it's the P-3AT.