It's the best of the three imo because it ties up the entire storyline. I'd recommend familiarizing yourself with
most of Lovecraft's body of work beforehand as Providence is heavy with references and easter eggs.
You may want to visit this site while reading each issue. I found it helpful in pointing out some references I'd missed.
I should caution you that there are some very graphic and disturbing scenes and themes. This is absolutely not a series for kids or young adults.
I'd recommend reading the entire storyline in order. I don't think any of them would make much sense without the rest.