Bipolars come in two basic types, high-performance with low-impedance windings
designed for constant current - use a chopper drive. Anything under 5 ohms is likely
to require chopper drive to be useful. Constant-current chopper drives often have
microstepping support - this is good, it reduces noise and resonance and increases
performance.
And then there are high-impedance windings designed for constant voltage drive via
H-bridge. These are much easier to drive but have poor performance at anything
but low speed. Typically 20 ohms or so for 12V motors, 50 ohms or so for 24V motors.