There are so many variables to this one. Long arms, short arms, high cheek weld, low cheek weld, etc. It all comes down to what you like and are comfortable with. Some stocks will be higher and will requires a riser on the optic. Some are very low and optic will mount flush. The stock adapter that you choose will also affect this. I like a stock that has a very fast connection to my shoulder and it can’t be slippery or small in that area. I also like a folding stock which allows for smaller storage. For me I went through a bunch and always end up going back to the Springer Precision Yugo adapter and Magpul Yugo/Zhukov stock. The combo is on their website and is very nice. It has an adjustable LOP but I just use it closed down all the way.
Do you have an adapter yet? Start there and then see what stock you like or go to the Springer web site and check out the combo I mentioned. I wouldn’t use the Sig folder adapter as it takes up a lot of length but that is just me. Thordsen (sp) makes a nice one. A stock on the MPX can end up being like a carry holster for your favorite EDC. I ended up with a drawer full of them until I found the one that FITS ME. Good luck.