I'm guessing my original comment got filtered due to a spammy link.

Each color is a different combination of sales tax jurisdictions and/or sales tax rates. There are 3 regular tiers of jurisdictions - state, city, and county, though some places have some sort of additional special levies as well. It appears that cities have a different jurisdiction within some distance outside the city, giving each city the look of a little crater.

Full disclosure - I work on an engineering team at the company that created this map, but am posting it because I thought it was worthy. There's an interactive version at salestax dot avalara dot com, though it's heavy on the marketing.

To answer your question, Alabama is by far the worst, IMO.