It depends on your goal. If you solely qant to get on the treadmill for the sake of getting on the treadmill a lo ger session will be what you want. Short high intensity is more of a workout and will help you achieve more of a fitness goal rather than a habitual goal.
I’m not an expert but in my opinion do both. don’t stick to one thing because you can get bored easily i know that i do. something you can do is do an intense workout when your ready and are very motivated but if you arnt the treadmill is just as good or you can do one day is a intense workout and the next day go on the treadmill. hope it helps❤️