Ditch that plastic thing that came with your espresso machine, or upgrade your ugly tamp for one of our precision barista tools.
Make sure you know the diameter of your portafilter basket. Most commercial standard E61 group espresso machines are 58mm, and the fancy precision portafilter baskets (IMS/VST/etc) can use the 58.35mm for a super close fit. The 58.35 tampers may fit normal 58mm baskets too, but if the basket is slightly out of round (or just out of spec) the tamper may hit the basket a little, or not fit at all. The precision baskets are made to more exacting specs and fit the slightly over-sized tamps every time.
Most of our tampers are flat bottomed, but tampers with a slightly convex face have their advantages, and we are intrigued enough to always have a few in stock. The convex shape presses a little more coffee to the edges, which can help with small single baskets and some double/triple basket channeling.
Wood handled tampers look and feel great, but can show wear over time in heavy use environments. Metal handles are more durable and easy to clean, but can look and feel a little industrial. Silicon and other synthetics offer interesting grip and feel, cleanup easier than wooden handles, and are available in a wide variety of colors. We also try to list the height of our handles with base attached.