Melvin Kidz posted in facebook:
Great question Melvin. Both devices are basically the same in features.
Arduino UNO Rev 3 and the SMD Rev 3 both have a microcontroller board based on the ATmega328. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started.
The SMD Rev 3 is moving more and more of their production capacity to surface mount ICs, the DIP packaged ATmega is becoming more and more difficult to get. To keep up with demand, it seem that Arduino now offers the Arduino Uno R3 with an SMD ATmega. The board is identical to the PTH version of the Uno, but you won’t be able to remove the ATmega without some hot-air.
To break it down the SMD version was originally a stop-gap when there was a shortage of DIP ATmega328s. That’s the only major difference.