Transistor to drive an ignition coil
Olin is right about the BJT. For power switching a power MOSFET is often chosen because of it's low \$R_{DS(ON)}\$, therefore it's low voltage drop, therefore it's low dissipation. 
Your requirements are not that high, however. 2A at 50% duty cycle is 1A average, a 200mV saturation voltage will cause only 200mW dissipation. Also, while there are logic MOSFETs that are specified at a few volts \$V_{GS}\$ they usually can only deliver a few hundred mA at that voltage. Most of the time they'll need 10V or higher to get > 1A drain current.  

A quick search for low saturation voltage transistors gets us a the OnSemi NSS40301, which has a maximum collector current of 3A continuous.  

  

The graph shows that \$V_{CE(SAT)}\$ at \$I_C\$ = 2A is less than 200mV, so average power dissipation is less than 200mW, far less than the 2W maximum rating. \$H_{FE}\$ is minimum 200, then you'll need at least 10mA base current.