I know most people prefer sterling crimps. I, myself, prefer crimp tubes, just a personal preference. So, the majority of the time I opt for sterling crimp tubes and they work very well.
But, what if you have a design that just does not include any silver? Say you have an antique brass or a gold piece to crimp. Do you typically still use sterling with those? Or do you use sterling and then try to cover the sterling crimp with a brass or gold crimp cover?
What looks good?
I usually will use one of three metals. Sterling Silver, Gold Filled, or Copper. All three will make a good crimp without fail. This is do to the fact that all three metals are soft. Also the thicker the walls of the crimps the better the crimp.
If you want to do something in another color, you could use crimp covers to cover the silver ones. Hope this answers your questions.
I agree with Sue on the three metals. I also have some fingernail polish in various shades/colors to dab the crimp when done if I need it to blend in.