Review on KESTER SOLDER 24 6337 0061 Solder 183°C by Elmito Yeager

60/40 solder works most of the time, but it can be in two states at the same time, solid and liquid, at temperatures close to its melting point (some may be solid, while some may be liquid). The 63/37 solder has only one state when melted, and some of the mix doesn't solidify until you're done. This makes it easier to get a "good" solder joint and is much more forgiving. It's not much more expensive than 60/40. Just make sure you buy the right diameter for your needs.