I think it's important to use both! I like to take pics of myself in pants or shirts that are a bit too tight, then a few weeks later take the same pic again. It's awesome to see progress in photo form. I took a pic of myself 3 weeks ago in a pair of pants that went on, but were too tight to actually wear out. I tried on those same pants yesterday and they fit!
I plan on wearing them to work tomorrow.
I also think using a scale is important too. It is difficult not to becomone "addicted" to the scale though. Obviously day to day our weight fluctuates due to water, salt... so maybe only weight yourself once a week. That seems to be a reasonable measure of progress!