I’m new to working with the GF, think I’m doing ok but I guess it’s all perspective. That being said:
I’m starting to work with acrylics, all new to me but that’s ok, you only grow when outside your comfort zone.
When engraving in transparent acrylics, is it best to engrave on the back for a smoother front or to engrave on the front?
I usually engrave on the back, but it really depends on what effect you’re going for. Try both and see which you like better. 
If I want it to look like an engraved surface I’ll engrave the front.
If I want it to look like an image behind glass I’ll engrave on the back.
*I will also always forget to reverse the image when I engrave on the back…which is fine unless it has words, and then I’m sad and do it over again.