Hey Christina, that's a little bit more of a philosophical question that goes back to how you've chosen to set up your lead scoring campaigns, but overall I would suggest that scoring is based on global campaigns and not set up individually by campaign.
The reasons behind this are for simplicity and sanity, as well as consistency. If you attached a lead scoring event to every campaign, you risk forgetting it sometimes, adding different values other times, and going crazy if you decide you want to change the point value of something somewhere down the line.
You can also better control the number of points that a person can get in a certain timeframe if it's global as opposed to local.
Hope this helps a little bit in your decision-making!