Lighter tires have higher rates of acceleration (neg and pos) because less rotational inertia. Even as little as 100g is very apparent if that weight is added or removed from the wheel or tire. The weight can vary amongst tires of teh same size a lot because of construction, flat protection, steel vs kevlar bead, etc. For example Panaracer Tserve 26x1.75 is 450g and the same size Crosstown is 1000g. The Tserv are pretty decent tires and when I went from 26x2.1 knobbies to Tserv 1.75, my bike was suddenly like a rocket.

Don't worry too much about the width. You just want something fairly smooth instead of knobbies if you intend to ride mostly on the street. Just don't go crzy on grass and gravel because smooth tires can't dig in and wet grass can be really slippery. Wet leaves and wood can be treacherous too.