I own a .40 and my roommate has the 9mm. Although the FNP 40 is much softer than other 40 calibers I have shot, I think the 9mm has less climb to it, but not by much. If that is the determining factor in your purchase, go with the .40. You get more stopping power with a negligible decrease in the control of the gun. I have gotten very accurate with the .40 esp during rapid fire.
I got an FNP45 and 2 weeks later I bought a FN9. Got to shoot the 9 Thursday. My buddy has a 40. The 45 has less recoil than the 40. The 9 is very pleasant and very accurate to shoot. I bought it simply because it's cheaper to shoot. If I can find a concealed rig for my 45 I will carry it. They are both reliable beyond words. I can't say enough good things about 'em. I have a 1911 45 ACP, FNP45, Baretta 92FS 9, and an FN9. Sure simplifys shopping for ammo.
Don't get me wrong here. That 40 is an incredible gun also.
FNP - Hi cap, target grade barrel. The undisputed MOST bang for the buck. Who could ask for more.
I prefer the recoil of the FNP-45 over the FNP-40. Thats not to say the recoil is strong with the .40, the .45 is like a slow "shove" to the rear while the .40 has more of the characteristic "snap" the round is known for. The FNP in both chamberings is a big gun and keeps the recoil to a minimum compared to some other pistols. The .45 is very controllable and with FN's downright brilliant idea of making it hold 14 rounds you aren't losing any capacity either.
If you really want a .40 caliber pistol, buy an HK. HK makes the .40 feel like a 9mm. Nothing handles the recoil of the .40 better then a HK USP as the pistol was designed around the .40S&W cateridge. Most other .40 caliber pistols are simply "scaled up" 9mm's. I really love the .40... as long as it's an HK.
In contrast, the Glock 23 in .40 is probably the "snappiest" .40 caliber pistol I have shot. It seems as if it transfers all the recoil directly to the shooter. I'll take my Glocks in 9mm and leave the .40 to other platforms.
The 9mm is the "bread and butter" and is pleasure to shoot. If it's your first handgun, whatever gun you purchase, get the 9mm. Cheap ammo means more practice. Also, the 9mm round is still perfectly adequate for self-defense as well. :?
Just took the FNP-40 out again shooting yesterday. Put another 160 rounds through it. I get better with every range session. I'm sure the 9 is easier to control out of the box, but you can get used to controlling the snappiness.