I am going to put Hardiboard on the back and the sides of my house, and putting cedar Shakes on the front. I am having a little bit of trouble on the way I should trim it. I am using smart board for all the corners but I don't think I should put smartboard on the front for the shakes. If I don't then you will see the edge of the shakes from the side. Need some advise on looks. I hope I have described it good enough.

You should trim just the front just as you did on the back and sides, then you can put the cedar on in the front instead of the fiber cement and the trim will match all the way around. The trim should all be the same color so using the smartboard everywhere should be fine.

I was just thinking that seeing the smartboard beside the cedar would look funny.

I don't think it will at all, once painted it will look the same all the way around. We do this on houses all the time, the siding may change but the trim stays consistent.