For years I have been using the 60/40 rosin core solder which consists of 60% tin and 40% lead. It is a great general-purpose solder which is easy to work with. It has a melting temperature of 374 degrees Fahrenheit and does not become a solid again until it cools to 361 degrees Fahrenheit. So you have a working temperature of 13 degrees. The down side to this is that components/ wires etc. must remain still during this cooling process or you will have a cold solder joint. I also have burnt my fingers many times holding wires during the cooling process. (Losing fingerprints in the name of tone.)

The 63/37 rosin core solder consists of 63% tin and 37% lead. The up side and down side about this solder is that it has no working time. It melts at 361 degrees Fahrenheit and it becomes solid at 361 degrees Fahrenheit. This solder works great for soldering components, wires etc. Because it cools once the soldering iron is removed. Less chances of cold solder joints. The down side of this solder is when you are de-soldering. You haven't any time to apply your solder sucker to the joint before it cools. You could use soldering braid to remove the solder. A method I like to use when de-soldering 63/37 solder is to heat the joint and apply a small amount of 60/40 rosin core solder so I some working time to use a solder sucker.