By no means am I an expert, but in my experience...

Pottery: You'll see pottery for sale in every city. However, the styles and colors vary significantly from town to town.

So it's not just enough to say, "Where's the best pottery?" My Mom loves the pottery markets in Rabat & Sale, but I don't like the colors available there. In Fes, all of the pottery has deep blue colors (sometimes with green & yellow accents), and you won't see "Fes blue" pottery in other places. While in Morocco, you'll see a lot of tadelakt walls--which is a plaster/lime finish. In Chefchouen I saw tadelakt-style pottery that I haven't seen in other cities, except at an upscale store in Meknes.

Jewelry: I'm only a gold buyer and given gold prices I wasn't shopping for gold jewelry on this trip. I did, however, buy gold in Marrakech on in 2004. Our guide knew I wanted gold & steered me to Marrakech. I can't tell you if that's because he got the best kickback there or the gold stores really are the best there. Because I haven't shopped for much other jewelry, I didn't notice regional variations. I'm sure there are some.

Silver: I assume you're looking for silver trays, teapots, etc., and not silver jewelry. Brass and copper seem to be much more common than silver, but I did stumble across a fairly large silver area within the medina in Fes al Bali (the old medina). My recollection is that it was toward the "bottom" (downhill) part of the souk near where the section that has a lot of pottery stalls. I haven't looked closely at silver, but assuming the market for it is similar to brass, my sense is that for new metalwork, there's much more uniformity in styles from town to town (unlike pottery). That said, the quality of new brass--and possibly silver, too--seems to be an issue. For example, I collect antique Moroccan brass trays. The old ones are heavy and hand-hammered. New ones are generally much lighter weight and the design is stamped/pressed into the metal. I haven't seen a new brass tray in Morocco that I've felt the need to buy, and when I've looked at Moroccan antique stores, the prices seem to be higher than on eBay.

Cloth: Again, not something I've bought much of, but I have purchased a few blankets, wraps, etc. in Marrakech and Fes. You'll see a lot of things woven from "silk" but much of it is actually what they call cactus silk, woven from agave. The cactus silk cloth availability seems to be widespread. If you're looking for more ethnic designs, availability is probably more regional.

These regional variations make shopping tough--particularly if it's your first trip--because presumably you'll only visit each city once on a trip. You have to make buying decisions on the spot without knowing what you might end up liking better/buying at your next stop.

In terms of sheer size, I loved the Marrakech souks located just off the Djemma el Fna. On top of that, the ville nouvelle in Marrakech has some very upscale Moroccan stores that were an interesting juxtaposition to the stands in the souk. Fes el-Bali is probably my second-favorite in terms of shopping. While I've been to Casa, Rabat, Tangier and Meknes, the shopping didn't wow me there. Chefchaouen is a great little town and the market is fun, but it's much smaller than the big cities.

One other note: You may want to plan your itinerary depending on what you expect to buy in each town. Leave the cities with heavy and fragile items for the end of your trip to help save your back & reduce the risk of breakage.