Between running in a slow pace but at that constant speed for a 30 min and running at high speed but get tired after 10 min, through which will you lose weight faster?
You will burn pretty much the same amount of calories running 1 kilometer really fast, as lightly jogging the same distance. When it comes to movement the distance is what decides how much energy you'll burn.
Running the 1 km will, however, be much faster than the light jog. If you only have half an hour to train you'll be able to squeeze more kilometers into that session if you move faster – thus burning more calories.
You might tire more quickly when going too fast, forcing you to rest and netting you less distance in the end of the session, than if you'd paced yourself. It sounds bad but this intensive training will increase you aerobic capacity over time and enabling you to go longer and faster as time goes by. This will let you burn more calories over the long term.
Short term – go only as fast as you can maintain movement throughout the whole training session. Long term – mix it up with high intensity interval training to increase your aerobic capacity.
If you are just looking to lose weight, you should do slow pace running. The point is to elevate your heart rate so that you are slightly out of breath and you will start burning fat.
You need to be consistent and do that several times a week though, along with a proper diet otherwise it will not have so much impact. Also don't overestimate how many calories you burn while running and do not treat yourself too much after each run (that's what many people do).
Remember that you need to be in caloric deficit to lose weight. Eating too much will defeat the purpose of the run.
Doing intervals (sprint-rest-repeat) won't hurt anyway, it could help you to vary your training a bit. Good luck !
The weight you can lose by changing your diet is much, much greater than the weight you can lose by burning calories by running or exercise. Exercise is great to keep your muscles in condition but not lose weight.
I have been doing both most of my life. In recent years I have been unable to lift weights or run as I had done, yet I can lose thirty to forty pounds as needed by modifying my diet over a five month period. Keeping it off for years has been a matter of building and using cooking skills despite life's demands on my time.