In my experience as a noob and layperson, coverts and cav twills are very similar, but coverts have a bit more sheen and appear dressier. Since I prefer matte fabrics, I tend to prefer cav twills. Coverts often do have more complexity/depth of color than cav twills. Ultimately both are great and possible even the best trousers. Flannels are so bound up with fall/winter, but cav twills and coverts can be light enough to wear year-round, with all the elegance, drape, and versatility of flannels.