The point of solder is to make a strong physical joint. 60/40 does that, flows better than any of the "specialty" solders, and you never get cold joints, tin whiskers, or other problems. I've found silver based solders not to flow or stick particularly well, so I've gone back to 60/40. Usually Kester, but Radio Shack is very good, as well.
Here is the article:
"In metallurgy, there is a special kind of alloy referred to as "eutectic". Eutectic alloys exhibit no plastic range upon melting, and the melting point is lower than that of any other alloy composed of the same constituents in different proportions. Stated otherwise, a eutectic alloy has coinciding liquidus and solidus temperatures, exhibiting a true melting point as is seen with pure metals, contrasted with the melting range seen with non-eutectic alloys. This allows quicker wetting as the solder heats up, and quicker setup as the solder cools. A non-eutectic alloy must remain still as the temperature drops through the liquidus and solidus temperatures, as any differential movement during the plastic phase may result in cracks, giving an unreliable joint. 63% tin / 37% lead (Sn63Pb37) is the eutectic alloy of tin and lead and has a melting point of 183°C (361°F), with no melting range as with Sn60Pb40. Sn63Pb37 was historically used extensively in printed circuit board (PCB) assembly applications, and we think it is easier to use in hand soldering applications as well."
Hope this is helpful.