Commander Shepard's first name is probably Sarah, or Jack
By default, Mass Effect's Commander Shepard is called "John" or "Jane", depending on your allegiance in the BroShep/FemShep war. According to BioWare's metrics, most players don't get much more creative than that.
After the defaults, the most common names chosen by players when customising their Shepards are, well, common names, BioWare revealed in a new blog post.
The graphic below shows the most common Shep names by gender, and also by country. It's interesting how little variation there is, isn't it? I think we've all gotten so used to generically-named video game characters that the moment we see a protagonist we want to call him Jack and sign him up for the space marines.
Officially, BioWare maintains that Mass Effect doesn't have a canonical default for anything you can make a choice about, so technically, Shepard doesn't actually have a first name. This list represents what her name probably is, all things considered.
However, on the subject of canon, Liara is definitely the default romance, amirite? I'm going to make BioWare admit this one day.