12VDC 10A Pwm Transistor?
Use a N channel MOSFET as a low side switch.  Since you have 12 V available, don't try to limit yourself to "logic level" FETs.

At 10 A, low Rdson will be very useful to avoid lots of dissipation.  For example, with 10 m&Omega; Rdson, the FET will dissipate 1 W when on and the full 10 A is being drawn.  The power dissipation is proportional with Rdson from there.

You will find a better set of tradeoffs available if you look at FETs intended for 12 V gate drive when fully on.  All you need is a FET driver chip between the logic level output of the microcontroller and the FET gate to generate the gate voltage.