Easy to make. A classic. Much depends on the gin you choose and I prefer it served with big cubes of ice, because they melt slowly, in a tumbler glass.
This drink should be all about the gin, so don't skimp on quality. I like Plymouth or Bombay Sapphire with tonic free of corn syrup. Glows under a black light. Cons: Commonly ruined by cheap tonic, too much lime or gin.