Should I do cardio or weights to lose fat?

Neither one burns fat the way people hope. Food decides fat loss; exercise decides what your body looks and works like as the weight comes off. A calorie deficit does the losing.

Within that, strength work is the quiet winner: it tells your body to keep muscle while the fat goes, so more of every lost pound is actually fat. Cardio burns a few more calories per session and is excellent for the heart, but on its own a share of the loss is muscle.

The practical answer is both, in small amounts: two strength sessions and some brisk walking or intervals each week, on top of eating a little less with enough protein. That is the whole formula.