I've done both.
- I started on just the scales and wished I'd taken measurements from the beginnning.
- I started the gym and took measurements, my scales were moving down slower and after a month I was glad I'd taken the measurements because I had lost inches and I realised it wasn't just about he scales.
- Now as much I would like to see a little more drop on the scales my main focus is the tape measure and shape.
Depending where you are on your journey I would take both into consideration AND take pictures front, side and back.