Gray and simple design like #100 #106 #124 are all very beautiful the only thing is not to fall into a standard graphics...
I would try to tell what I like from all design
#45: very good the balance between gray and blue, and also the back side is very well
#78: good idea of orange that starts from the blue, and very good place of the data on the front side of business card
#106: very good url place and very well back of business card
#124: very beautiful colors and the orange curve, also the url place is very well

I do not know if this can be useful ...