Tennsy Arduino compatible board series are great small boards with native USB. There are two major branches Teensy 2.0 and Teensy 3.0. First one is based on Atmega USB chips while 3.0 series comes with ARM Cortex microcontrollers. Recently a new Teensy 3.1 board was introduced. This is same form factor as Teensy3.0.
When Comparing Teensy 3.1 to teensy 3.0 we notice that microcontroller speed increased from 48MHz to 72MHz, RAM increased from 16K to 64K. Flash memory also doubled to 256K. It now has 5V tolerant digital pins. Among other features there appeared CAN interface, 12 DAC. So, practically power is doubled with pretty much same price tag.