Color Print quality 30 x 20 metallic

Mounted display prints (30 x 20, metallic paper) for a gallery series, I'm getting prints from Miller's Pro Lab in Columbia, MO., and prints are generally very good (smoothness of mounting on foamboard sometimes an issue) - but are there noticeably better image-printing techniques or machines available at other labs?

Is there any - definitive reason - why one lab is better than another? Or which lab machine or process delivers - noticeably better - colors or sharpness? (Service is not an issue, Miller's is very good, fast delivery is exceptional) Has anyone done an honest comparative of labs and resulting prints?

I had good success with ColorInc Prolab. They mount on gatorboard and styrene. Their prints come very well matched to my home printing also.