Actually, the PA heals faster than the frenum and it is definitely not less hygienic (as mentioned by one of the other respondents):
Bodily fluids are apt to get on certain genital piercings, like the PA, which is not a problem—if they are your own. Urine is one of man’s first antiseptics and, if you are healthy, your own liquid waste will not harm your piercing. The regular passage of urine over the jewelry helps to minimize crusting, too.
But what's more important is which appeals to you the most. Personally, I find there's more sensation from a frenum piercing (especially one on the top, rather than the underside).
There are lots of other piercing placements to choose from, too. For loads of information about all of the piercing options (including how to select a qualified piercer), check out The Piercing Bible--The Definitive Guide to Safe Body Piercing (Random House, May 2009) by Elayne Angel.