Which motors to choose? I don't know if this is the right place to ask, but I'm an arduino newbie and I'm seeking some suggestions.
For my Robotics subject at University, I'm going to build a robot that should be able to move some objects (dragging them on the ground, not lifting them) from one place to another. I was looking around the web for the necessary components when I stumbled on a doubt: are 3-6V motors powerful enough for the wheels? Or do I need something more powerful like the 12V motors? 
I'm not sure of what to choose between step motors or servo motors either, what do you suggest?
Oh and last thing, I opted for a L293D bridge driver for the motors, is this a good idea?

Thanks in advance!
A 12 volt DC motor is good for dragging items, but then again it depends on the items weight. Stepper is used for millimeter precision, like 3D printing. Servo is an DC motor with precision for 180 degree movement, like robot arms. If the moving object is over 1kg you should look into geared DC motors or even the stronger brushed motors, or geared brushed motors. Whats the max weight?