WHICH ONE SHOULD YOU BUY? You're looking for a soldering iron but not sure which one is best for your purposes? Here's a quick run down:
Electric: Nice because they don't make noise or fumes like the propane and acetylene. Also, you don't need a hose and tank and if you're out on a job, the electricity is usually provided for you. They have a half hour warm up time and don't work well in cold and windy situations. They're ideal when soldering inside the shop or during warm summer conditions. The American Beauty 300 watt is good for all around soldering. The 550 watt is better for flat lock work because it's bigger and heavier, but may tire your hand if you have to hold it up all day (when soldering flat-lock, the iron is resting on the work). Get a complete kit if you have the money.
Propane and Acetylene: These irons need tanks and hoses, but burn hotter under all kinds of conditions. They're a must if you're going to solder in colder and windier conditions. The propane units use tanks that you can buy almost anywhere, typically used for barbecues. The acetylene tanks you have to find at a gas dealer. These units do make some noise and fumes. The Sievert Propane Irons are a little bigger than the Express Propane Irons and have bigger copper bits so they're nice for flat lock work. The Express, being a little smaller, fits into tighter spaces better (such as inside gutters). You can't go wrong with either of them. The acetylene irons are good and hot too and many contractors swear by them.
Portable Irons: The portable irons are great if you just have to do some quick soldering and don't want to fire up a propane rig or wait for an electric iron to heat up. They're also great for carrying up on a roof to do some quick soldering because there is no tank or hose. Each gas canister only lasts an hour, but when you need it, these portable devices are wonderful to have.