Tire profile shape and tread pattern probably plays as much a role as tire size. And 'upgrade' is a word thats thrown around quite a bit, but just changing tire size isn't necessarily an upgrade.

Better tires have higher thread counts, compounds that both grip better and last longer, and in most cases they actually weigh less at the same time. But they cost more too. What's your budget, what do you have now and whats important to you?