my 2 cents...
i have/had all three of the firearms in question: the XD45-compact, the m&p45 mid (recent stolen actually); FNP45 (stainless). all 3 are fine firearms and i would say that the m&p was my least favorite of the 3. so far i shoot the best with the XD45, that is likely due to familiarity with the XD and also because i have just been shooting it better. i have only fired the FNP45 about 100 rounds, compared to about 2k on the XD45. i will say that i shot just as good if not better with the FNP on my first experience with it and truly believe that i will be better with it after another 200 to 300 rounds, no doubt. the FNP really does feel like a 9mm, no BS. i was skeptical but change my tune after about 15 rounds. the DA trigger is a beast, but the SA is very short and crisp...almost scary.
with regards to size, the FNP45 is a bonafide tank...in every way a handgun could be. and that is not a bad thing either. this is not a gun for those who want something ultra concealable or worried about printing when carrying concealed. the XD is longer as the barrel is 5" and the FNP barrel is 4.5", but overall the FNP is just a bit shorter. its a nice length that doesn't make the gun feel too long, i think that the XD tactical is too long for my taste. the FNP slide is heavier, it feels like your holding and impact weapon....lol. but overall the FNP is a bit heavier than the XD (compact & tactical). it is definitely heavier than the m&p midsize. the weight of the FNP is very balanced and distributes well, you dont notice it that much until you field strip and hold the slide by itself...the frame is super light. the m&p is definitely the slimmer of all 3 guns and the shorter. it also has the most recoil and is the least accurate (IMO). the FNP is smaller than both the HK USP45 and that Glock 45 in comparison. so don't be fooled by those who say that it is too big, it isn't. i may very well be the best polymer 45 on the market....although the new HK45 gives it a run for the money (also cost nearly 2x as much).
if you are not worried about concealing the firearm and more concerned with capacity & build, i would put them in this order:
1) FNP45
2) XD45
3) M&P45
if concealment (size) is an issue:
1) XD45 compact (10 to 13 rounds of 45...nuff said)
2) M&P45 midsize or compact (although it is smaller than the XD, not much)
3) don't go with the FNP...find another gun (maybe go with the taurus PT-145 Pro, if it were in the conversation i would move it to #1 or #2 here)
if you look at accuracy and recoil (low), then:
1) FNP (the weight of this gun makes the difference)
2) XD
3) M&P
ergonomics and overall feel (grip):
1) M&P
2) XD
3) FNP (would tie XD if not for super rough checkering on the grip)
looks...come'on, you know we care how kewl it looks, lol:
1) FNP...just a bad ass lookin gun. kinda like a chevy avalanche...
2) XD and M&P (tie)
if you want the best all around polymer 45 and the most for your money (IMHO)....then go with the FNP 45, you will not be disappointed. i love all three guns, you really can't go wrong. get them all if you are a 45 fan, just spread it out. they are all good guns.
on a concealability note, both a friend and myself have been able to conceal the FNP well. it takes a change in your attire if you wear really fitting clothes...im a big guy and wear everything loose. i would do IWB in the summer and OWB in the winter with it. my FNP came with the shooters pack, which has a blade-tech belt/paddle holster included. the length of the FNP isn't really the issue at all, the real issue with regards to the size is that the FNP is a THICK gun. the slide is well built, but thick as a brick. the grip is fairly think as well, but i didn't find it too difficult to get a proper hold on it. i have short fat hands, average length likely, and find it ok for me. my partner has large hands and he feels like it was made for him.
the best thing to do is to handle it and maybe try it in a holster if there is one available that fits. one thing to remember is that this tank holds a total of 15 rounds!!! so add that to the weight if concealing.
my FNP cost $575, stainless with the shooters pack and other goodies.
p.s.: that yellow plastic barrel is actually a training barrel...lol.
