PWM stands for "Pulse Width Modulation" and is a good technology based method of speed control increasing the efficiency of the motor it is controlling.
Smart Speed Control can mean anything depending on the technology used. This is one of the terms used by creative product marketing departments. Check into how the speed is controlled in these instances.
Given a choice, I prefer PWM motors.
Then maybe you know why my PWM don't work after install new cooler (hyper TX3 with 4 pins and PWM) with stock cooler PWM control work well (when temps go highter fan speed is 2500-2800 RPM in idle is 2000 RPM), but now fan speed is only 100% 3000 RPM and don't change on highter temps. Only if i set in BIOS Smart Speed Control then change yes, but only with bios setting.