Single flute upcut bits which state they are designed for acrylic. Carbide uncoated bits work well and stay sharp. For the pieces illustrated below, I used an 18,000 RPM spindle speed with 1mm stepdown, 50% stepover and 1500mm/min feed speed and held the parts with four 2 x 1mm tabs. The rotational speed ensures an efficient cut at speed and moving the cutter through the material quickly ensures that the acrylic does not melt onto the cutter.
Also consider how much lateral load you are placing on the cutter. It is always worth testing your material with your selected values and watch the cutter’s progress. Listen for any noises that indicate the resistance of the material to the cutting values selected. If anything sounds laboured, it is and it will shorten the cutter life, dull the cutting edge and potentially break cutters early. In my images, you can see how an effective choice leaves you with sharp, finished edges.