I think there may be some confusion over terminology here. The Lichuan servos that Dean linked to are generally known as "AC servos" and don't need a separate psu - they take 220V mains directly. The term "DC servo" is not clearly defined but generally involve brushed motors ie an H bridge output and a 2 terminal motor. These aren't used much these days.

You might also talk about "brushless DC servos" (BLDC) which are pretty much the same as an "AC servo" but they drive the motors with a trapezoidal 3 phase voltage rather than the sinusoidal one seen in an AC servo.

The various open and closed loop steppers have 200 or more teeth per rev, whereas an AC servo is likely to have only a few poles per rev.

An AC servo motor will be more power dense than an equivalent AC induction motor (VFD etc) and also more power dense than a stepper. AC servo and AC induction will both create a fairly flay torque speed characteristic, whereas the torque from a stepper falls off quickly with speed. Gearing down a stepper "to increase the torque" may not actually gain you much / any torque in some cases due to that torque fall off, unless you are focusing on stall torque.

As Dean says, there's a lot to be said for going AC servo and those Lichuans are very keenly priced. There's no right or wrong here but that's just some input from my side. I develop motors and inverters in my day job and (sadly) use them from time to time in my workshop.