I'd go with a .357 magnum because the energy is so much higher than the 44 special and it's a proven man-stopper. If you like the NightGuard line, I'd go for a model 327 8 round or a 386 7 round.
If you like the idea of big heavy lead, then I'd go for a .44 mag over a .44 SP since you can always load the mag down if you want. The mag is bigger than the specialin the NightGuard line, since it's a 6 shot cylinder instead of a 5-shot cylinder.
If you wanted concealment and that's why you were thinking of a .44 special nightguard, you could go with a 5-round model 60 in the J-frame or a model 340PD 5-round in the scandium alloy j-frame both chambered in .357 mag.
It all comes down to what you want and whether or not you intend to conceal it.