I've worked both now - the Anniversary billing for the longest - there were very few times when we had to adjust their payment date due to their pay days. We did not pro-rate in or out there. They paid the full month and their payments were requested on the anniversary.

Now that I work the 1st of the month, we at least have most of the income at the first of the month and don't have to go to the post office with the certified letters at different times throughout the month to make sure they make it out in the specified time......but you also don't have many payments come through throughout the month..........