Saber is bi with a preference for girls judging by how she acts but um yeah.

... Also main Saber, Saber Lily, and Nero(though she is a different character) are the best Sabers.

Saber Alter is nice too though.

Also Saber is amazing, and, um... explaining her would be a bit hard to do quickly without potential spoilers but I suppose the biggest spoiler is actually pretty well-known, but, um...