FWIW: I have an early (11/78) P6 that I really like. The only problem is the DA trigger pull. The Germans spec'd a very heavy DA pull. The DA pull can be fixed with a $5 P225 mainsping from Midway, or Wolff makes replacement springs in different weights. I think a package of several weights runs about $12. However the SA pull on my P6 is as good as the smoothed, but not lightened, SA trigger on my S&W 10-4 revolver. Very nice.
Also, while some pre-1982 P6s have trouble with HP ammo mine doesn't. I think it was rearsenaled in about 1988--the grips are dated 1988-- and I suspect the feed ramp was changed at that time by a German smith. Check the date on the one your looking at. If it is post 1982 it should eat any ammo you put in the mag.
Overall, my P6 is rock solid, functional and accurate. No misfires, no mag problems. It has nice weight and balance. I have no complaints. I live in Illinois so we don't have CCW, but, if we did, I'd install the P225 spring and carry the P6.
That said, I've always liked the 39-2. I've never owned one, but the ones I've held fit my hand well, much better than the 59 series or later S&W semis, (although I do like the M&P semis). Choosing between the two is a hard decision. The 39-2 is a more attractive gun--the P6 isn't beauty queen. If I didn't have the P6 already, I might pass the P6 by because of looks. I vaguely recall from the 80s that some 39-2s had problems, but I don't recall what the problems were--and no gun design is perfect. Either would be a good choice.