It is the successor of the rpi 1 series.The major reason to pick this one other than rpi 1 series is that it uses 4 x arm cortex processors and BCM2836/2837 which increases the speed much more.
Specification of Pi 2 B/B 1.2v:
Audio and display: HDMI port(1080p video out)
Broadcom Soc: Broadcom BCM2836(for 2B)
Broadcom BCM2837(for 2B 1.2v)
Processor: ARM Cortex A-7 x 4(for 2B)
ARM Cortex A-53 x 4(for 2B 1.2v)
Processor speeds: 900 MHz
GPU: Broadcom VideoCore IV @ 250 MHz
Ram: 1GB
Input: Usb 2.0 x 4
Power: Micro usb type B(5v,2.5A),GPIO
Usb otg port: None
Ethernet: 10/100 Mbit/s
Wifi: None
Bluetooth: None
Video input: CSI camera port
Usb port: 4
Audio in: Revision boards through I²S
Audio out: 3.5mm audio jack port,HDMI,I²S
Video out: HDMI,DSI display port,audio jack as RCA jack,GPIO
GPIO port: 40 GPIO headers(compatible with hats)
Reset: Software reset
Power consumption: Idle[230mA]
Video 1080p[290mA]