Basic self colors, black, blue, chocolate, lilac are the easiest to work with because there are very few color faults you can run in to, there aren't really different shades that might be more or less desirable than others like there is with basic agouti colors, and the main problem is just keeping a dense enough coat. You often want to cross your chocolates and blues back to blacks which tend to have thicker coats from being bred for quality longer than the recessive versions.
If you want to get in to harlequins do a ton of research in to the proper pattern. The whole rabbit has a certain pattern to follow and finding good breeding stock and making good show stock can be quite difficult with this color.