How to drill a hole in plexiglass (acrylic sheet)?
You do not specify thickness, so I'll take a guess at 1/4" or thinner.

The problem with drilling plastic is that conventional bits will "catch" on the plastic, pulling the bit into the hole with more force than desired, typically cracking the plastic being drilled.

Using step-up method to drill the hole will not eliminate this problem.

Lacking the aforementioned hole saw, the spade bit is a better choice. I have Forstner bits but have not considered trying one on plexiglass. If you have a drill press and the increased control it offers, you may have good luck taking small bites with the forstner. The cutting edge of a forstner bit is more like the edge of a plane and may also dig in too quickly otherwise.

Drill bits designed for plastic have a much sharper angle. A set I recently purchased has an abrasive material on the cutting surface as well as a subdued cutting angle, effectively abrading the plastic and lifting it to the surface.

I overlooked your option of a step drill which is the best of the list. Each progressive cutting edge will not gouge into the plastic as much as any of the other available choices. Again, a drill press improves your chances of a good result.