I have a S&W M&P 40c starting to reload and would like to know the best powder to use

There is no "best".
First step is to read the fundamentals section of a good reloading manual or three.
Then decide the purpose of the load you want to make.
Then select the bullet you want to use, and decide how fast you want it to go.
Then go to the data section of your manual and select a powder you have (or can get). That is suitable.
For 165gr or 180gr bullets in .40S&W, there are a dozen powders that will work: most of the medium powders, and some of the faster powders for lighter loads.

I personally use HP38 and Titegroup for major power loads with 180gr bullets for USPSA.

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Science plus Art

You will get a lot of recommendations but it really comes down to your parameters and likes and dislikes . OKFCO5 gave you some good advice.

We have a great reloading sub forum, check it out sometime.