Lead free solder can be much harder to use, but the exact metallurgical formulation can make a significant difference in how the solder behaves. In my experience, the more inexpensive tin-copper lead-free alloys can be problematic, so for a two metal alloy tin-silver is usually preferable. I've also found some of three (like Sn 96.5%, Ag %3.0, Cu %0.5) or four (like Sn 96.35% , Ag 3.0% , Cu 0.5%, Sb 0.15%) metal alloys, have a better performance as a general purpose solder. However, they are usually almost three times the price of tin-copper.