Apex vs Pro trigger...hard to say. For me personally, I'd rather go and stay with factory than to make a change but that is me. The only thing I add to my guns are extra mags; I tend to not have good luck when modifying anything and like Clint Eastwood says "A man has gotta know his limitations..." and that is mine.
It's hard to say the exact reason I like the 45's trigger over the 9 Pro...I actually have more rounds through the Pro at the moment, but the 45's round count gets higher and higher each month. It is honestly hard to say and it could be several factors combined in making the M&P45 feel better to me than an actual tangible thing like trigger weight. I think too much grief is given about the M&P trigger; it is light but consistent. I had my last 2 Glocks with me at the range along with my 2 M&P autos and did nothing but concentrate on the triggers and every time I came back to both M&Ps liking theirs above the Glock's.
I know that might not be exactly what you were hoping for; the quality of the trigger is kind of a personal preference and I don't think the Pro is that big of a leap above the standard models. It is the night sites or fiber optic sites in addition to no mag safety and no manual safeties than also help put the Pro above the standard models but again, there is a lot of your own personal preferences in there.
My personal preferences are actually thumb safeties...sounds silly and on anything other than an M&P I'd probably balk but my M&P45 came with one and I love it...in fact when I bought my M&P9c I probably paid a bit more for it but it was from my little local shop and it had the thumb safety so for me, I'd buy an M&P9 with the thumb safety and add night sites later but again that is me.
