Wheel Question

Is it just me or when I see pictures of 19" wheels on the clk they look perfect on the back but in the front they look a bit big? Would it be dumb, risky, etc to put 19 on the back and 18 in the front?

Also, I have read that 35 offset front and back is good, but I have also seen people using 28 on back and 32 up front....bad idea?

Thanks for your time.