Best Solder

Welborne Labs house brand is better than WBT and as good as and cheaper than Cardas (which they also sell).

http://www.welbornelabs.com/solder.htm

In reality the silver content in the solder or the absence of lead doesn't make it best.

The best solder should be the best for its particular application.

If you're about to build-up a solid state equipment(or work with OpAmps or ICs) than the temperature applied to the device leads is crucial. Therefore it's not desirable to have a solder that has high temperature of melting such as tin-silver solder. Any solder has very poor conductivity compared to the cooper or silver therefore its function is to hold conducting leads together tight. A content of silver in the solder only makes it to melt under the higher temperature and so higher power device should be used to work with such.

A lead-free solder has an advantage not to be as harmfull for the human flora over the one that contains lead. Despite that any soldering job should be done with good air circulation and avoiding inhalation of the flux and solder smoke.

The "speed" is the most important factor that I value in solder. The faster I join conducting leads the less I inflict them under the high temperature the less I stress the conducting material and device I work with. Becides the above mentioned speed I also love the ability to leak. Hard tin-silver ones can't do that and can form bubbles if not sufficient time applied to melt it. Therefore I figured that spending 5x or more for Cardas or Johnson ain't worth it(too damn "slow") and chose Weller.

P.S. Always remember to join conducting leads and NOT solder to solder!

I would second Nsgarch's recommendation for the Welborne Labs House brand. It's the easiest to work with that I've found, inexpensive and I certainly can't hear any difference between it and other solder.