There's only so many to choose from;
PM63
VZ61
Uzi Pro (finally small enough to not quite qualify as an SMG)
PS90/P90
TMP/MP9
Stechkin (I guess)
MP7
M3 Carbine (I guess, with para stock and shorter barrel, maybe)
That non-suppressed SBR version of the VSS Vintorez (on the big side)
SIG MPX (still kinda on the big side)
I personally think it's the most unexplored, and therefore
interesting field of firearms development left. It's the peak of engineering difficulty to pack all the features of a larger weapon (controls, locking, and feeding systems, and sights) into a very small package, which is effectively what the PDW is.
You have to simultaneously optimize:
-Size (not too big to be unobtrusive, not too small to be ergonomic in F/A fire)
-Weight (by using small high pressure cartridges you can retain desired firepower)
-Feeding (maintaining full auto reliability with small ammo is more difficult)
-Features (manual safety, selector switch, charging system, modularity, sights)
-Strength (by incorporating a mechanical locking system that allows for higher pressure ammo)
-Cool (laugh all you want, but the quintessential PDW guns all have some unique quality that constantly lands them in movies/games/etc.
)
My personal belief is the MP7 is the only modern gun to truly fit the niche (even the P90 more resembles an SMG in its simplicity), and the M3 Carbine before that. Most every other weapon has been either a lower powered pistol caliber carbine (TMP) or a much more powerful light carbine (Vintorez). The M3 Carbine in 22 Johnson Spitfire w/ short barrel and folding stock would have been right on the money
TCB