I know I'm asking a question from a biased audience, but honest and unbiased responses, please. I'm on the fence here. I've owned the G30 in the past and found them to be too thick for concealed carry.
The difference in thickness between the M&P 45c and the G30 is about the same difference as a G30 vs. a G19. In fact, the M&P 45c is almost the same size as a G19. It has a slightly longer slide and a slightly shorter grip. The thickness is pretty close to a G19.
The grip on the M&P is also noticeably thinner (8 rounds vs. 10 in roughly the same grip length), but I realize that doesn't matter as much for concealment. Personally, I would buy the M&P 45 between those two choices because I like the feel.
The Glock 30 is thick but I shoot it better than any other ccw hand gun so I dress around the gun. It may take a few trys to get the right holster/belt/location/concealment garment combo. The gun is only one piece of the puzzle. I find that folks don't try hard enough to find that magic combo. I feel its worth the effort to carry a gun that really is not that big and shoots so well. something to think about. Good luck and I hope you find what works for you my friend.
I already own a G36 and love it, just considering my options. Both pistols were ordered by my LGS so I'll make my mind up once they come in. The MP45 Compact is shipping now, so I'll hopefully get to see it in a few weeks. If the MP45 Compact conceals as well as my MP40c, it will be the choice made. Although I love my Glocks, I like the way the M&P line feel.