Should I use an eyebrow pencil or a brow gel?

They do different jobs and many reviewers use both. A pencil (like the Anastasia Brow Wiz or Maybelline Total Temptation) adds hair-like strokes and fills sparse areas, while a gel either tints and adds volume (e.g. e.l.f. Wow Brow) or simply sets brow hairs in place (clear gels like NYX Control Freak or NYX Brow Glue). For sparse brows, a pencil first then a setting gel is the common verified-purchase workflow.