Sweatshirt is great when its winter time!
They are, they give you a sense of warmth and comfortability. 
Do you have any recommended brand that offer comfortable sweatshirt? 
I think Nike and Adidas sweatshirts are extremely comfortable. 
Are they comfortable even in summer weather? Wouldn't you get overheat?
You can get a little warm, but as long as you stay hydrated and don't be in extreme conditions, the heat is worth the comfort. 
Oh great, do you think the color of the sweatshirt have an impact on heat? like white or black?
I have always heard that darker colors will absorb more heat, so that is something to take into consideration during warm times. 
Although black looks cooler, wouldn't white get weird stains? 
It's definitely a possibility, and I recommend taking it off if eating messy foods.