Acrylic vs. Epoxy Silkscreen?
Acrylic silkscreen is generally printed onto the PCB using effectively an inkjet printer. Epoxy silkscreen is generally applied using a wet film. Acrylic is generally UV-curable, whereas epoxy is generally baked.

In my experience, acrylic silkscreen tends to be a cheaper, less time-intensive process, but the quality is not as good. If you look closely at the printed silkscreen you will generally see the different "pixels" and jagged edges, and will make small text much more difficult to read. Epoxy silkscreen tends to be much smoother, but is a more expensive process.

Here is an image showing the difference between the printed silkscreen and the wet silkscreen:



Image from Dave Jones' EEVblog video, https://www.youtube.com/watch?v=rEB0pl8a5C0

And here is a comparison chart from http://blog.optimumdesign.com/toward-a-more-rational-silkscreen :