The last month of the year has a boost (December).
The last month of each half year has a boost (June and December).
The last month of each quarter has a boost (March, June, September, and December).
So, December is the best, then June, then March and September.
The first month of the year has a drop (January).
The first month of each half year has a drop (January and July).
The first month of each quarter has a drop (January, April, July, and October).
So, January is the worst, then July, then April and October.
February, May, August, and November are in the middle.