This weekend I picked up a P-32 and I've owned a Guardian for a couple of years.  After a trip to the range to compare them side by side, and carrying the P-32 for a few days, I conclude the following:
1.  In every respect, except weight, the Guardian is the smaller of the two.  The P-32 is light and thin, but it is longer and taller than the NAA.  If you want to carry in the pocket of running shorts, the P-32 has a slight advantage for that reason.  The difference in weight is small to start, and narrows a bit when both guns are loaded.  With a full magazine, the P-32 isn't as remarkably light as it feels empty.
2.  My Guardian and P-32 are equal in practical accuracy.
3.  Recoil is about the same in both guns.
4.  The Guardian is a much handsomer and more nicely constructed gun than the Kel Tec.  It is also more expensive.
5. No reliability problems with either gun.

Final verdict?  The Guardian is generally a classier pistol.  The difference in weight is a matter of a couple ounces, if that is critical to you, then buy the P-32.  Of the two, I'd say it is also more likely to retain its value.  I'll be carrying my Guardian in preference to my P-32 most days, I expect.