On a session by session basis, “cardio” training will burn more calories in an hour then a strength training session.
However the calorie burning effects and benefits of cardio training end as soon as the workout is over. Strength training workouts on the other hand have been shown to increase metabolic rate for as long as 38 hours after a workout is completed.
Strength training also has the added benefit of building muscle. The more muscle mass you have, the greater your basal metabolic rate (BMR). Your BMR directly impacts how many calories you burn at rest, meaning someone who carries more muscle on their frame will burn more calories than someone the same weight with less muscle.
Your BMR accounts for 70% of your total daily caloric expenditure! A 1 pound increase in skeletal muscle mass equates to approximately 50 extra calories burned per day. This doesn’t really sound like much, but by the end of the year this would add up to over 5 pounds of extra weight loss, and this is with a 1 pound increase in your skeletal muscle mass.
Weights are also anabolic in nature and force the body to adapt to the strength demands placed on it. This is why if I had to choose one or the other for weight loss I’d pick resistance training every single time.
This is not to say that cardio training is bad. There are obvious amazing benefits for heart health an longevity. This is simply weighing the option of the two for weight loss. An ideal program would combine the two but I always put a premium on the weights!