No contest:  I prefer traditional silver solder (cut into paillons with tin snips, and used with borax flux) over solder paste.  The paste is expensive, dries out easily if the cap's left off, and in my view, just doesn't produce as strong a solder joint.

Having said that, it does have it's place:  solder paste is very easy for beginners to use (though it's well worth learning how to solder the traditional way), and can be quick and easy for solder joints that won't take much strain (for example, soldering closed jump rings).

We teach both methods here at the Sussex Jewellery School, so you're best equipped to choose whichever method will be best for your soldering operation.

We love teaching you how to solder - Sussex Jewellery School courses that include soldering skills are:
Soldering without Tears (1-day)
Enamelling on Fine Silver (2-day)
Silver Rings Intensive (2-day)
Silver Jewellery Intensive (2-day)
Fingerprint Jewellery as a Business (1-day)