I would say that "-" is better for users. The minus/dash is a "regular" character they are more likely to have come across and know the location of the key.
Stack Exchange uses the "-" to separate the prepended tags from the actual title. This question is:
seo - Which symbol should I use in Meta Title: “|” or “-”? - Stack Exchange.
The Guardian uses "|" to separate the title from the name of the paper:
Latest news, sport and comment from the Guardian | The Guardian
Given that both sites rely on SEO it clearly doesn't matter which you use.