Own both.
The 9c feels a little better in hand, but the 19 shoots better (in my hands).
They both conceal pretty much the same. If I am wearing something that I can conceal the 9c, I can also conceal the 19, but I always use the mag with the pinky extension on my 9c. I don't use the flat mag. I prefer my glock 26 to the 9c with flat mag.
If I could only own one, I would keep the 19.
You can't go wrong either way, both are outstanding pistols.
Bottom line, the 9c is an in between size in my opinion and isn't that useful for me. It does have slightly better ergos but not enough better for me to make a switch.
Now, if S&W made a M&P exact size and capacity as a 19, I would probably switch if I shot it just as well.