Hi Daryou,
For flat pedals with "grip pins", the best shoes, IMHO, are those by Five Ten. I ride Freeriders, and they have almost uncanny grip, and are fairly stiff. Also, because of the generally large surface/contact area of flat platform pedals, shoe stiffness is not all that important.

I should also mention that I periodically use trail running shoes when riding. Most athletic shoes of this type have lots of ridges and nooks that can grab on to the aforementioned pins for good grip.

Best of luck!