Does it matter which workout you choose on Apple Watch?
Yes it absolutely does.
Your apple watch doesn't just calculate your calorie burn based on your heart rate, it has an algorithm for every type of exercise that uses your heart rate to work out your calories.
HIIT vs cycling for example - you can get you heart rate to the same place but physically are going to burn more calories doing HIIT than cycling.
So make sure you pick the right workout!