I have a spool of PETG that I plan to use for most of the parts. However, I would like to print some of the CNC out of PLA and avoid ordering any more PETG. I was thinking the feet probably don’t need to be as strong. Any advice on other parts that might not benefit from the extra strength PETG provides?
PETG is tougher as in it flexes more before breaking, PLA is more rigid. For the most part it does not matter but I suggest at least the XYZ be PLA. Then you run into printing and shrink rate differences. If you are not confident I suggest sticking with PLA.
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I didn’t think about that. I want the machine to be rigid not flexible. 
I actually printed my first set in PETG, and to me it had too much flex. Hope this helps.
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I am able to get my cheap but highly tuned (Ender 3) printer to print both PETG and PLA parts to tight tolerances. So I am not really concerned about shrinkage. PETG feels like a stronger part but it does flex more. On top of that the PETG is more expensive so I am going to use it for other projects. I have decided to go with PLA. Thanks for the help.
I printed most of my parts in Matterhackers Ryno for my first CNC that isn’t built yet. Ryno is a type of PETG with some differences.
A lot of my parts are petg with 4 perimeters to make up for some of the flexiness. So far no issues, and nothing has cracked like the pla did last winter.
When I printed my 4 carriages in Matterhackers Ryno I had too much layer compression in Z. I did use a different printer for those with a 0.6 nozzle. The other parts I printed in Ryno seem fine. I re-printed the carriages in Matterhackers Tough PLA and the dimensions are right on. If I ever get my tubing I’ll be reporting my progress/issues. I have been using 3 perimeters for everything whether PLA or PETG, and 0.28 layers.