For me it's like asking "What's your favorite child?". As a curator of a nice collection of elements, I have a really difficult time picking out a "favorite". So I'll just list the ones that really pique my interest with a brief explanation of why.
Bromine: The intensely dark color, pungent odor, and the fact that it's one of the few pure elements we see in a liquid form.
Cesium: It has such a beautiful golden color to it and forms amazing crystals when it solidifies. However, the metal will melt just barely above room temperature so when you hold the sealed ampoule in your hand, you see the metal melting right before your eyes into a beautiful water-like golden liquid.
Uranium: Most people on this earth have never seen or held the pure metal in their hands. It tarnishes readily like neodymium above it, but it's incredibly dense, incredibly hard, and makes a geiger counter go nuts when it's put near it. All you hear about it is that it's radioactive so many people fail to recognize the fact that it's a metal just like iron is.
Osmium: A truly 'colored' metal that is incredibly dense, resistant to oxidation and readily oxidized at the same time. Just the way the metal is formed determines the reactivity. Solid lumps like what I have in my collection do not oxidize at all. A powder or sponge version of the same metal, however, readily oxidizes into a horrifly toxic and putrid smelling oxide. (Mine isn't oxidizing because it is totally odorless). It's amazing how the form of the metal can alter its chemistry so much. In addition, the blue color of it is as unique as it gets.
Gold: It's a wonderfully colored metal which is as soft as can be, yet incredibly dense as well. Many people don't realize just how dense gold is until they pick up a sizeable mass of it. Then their eyes light up as they see how much mass is in that tiny little gold slab.
Phosphorus: A VERY reactive element depending on the allotrope you have. White phosphorus goes crazy with just about anything. Red phosphorus needs some motivation to get nuts. Black phosphorus will barely react at all. All the allotropes are so different from each other, yet amazing in their own rights.
There are so many more that I could wax on about for years, but these ones just stick out in my mind at the moment.