Don't compare her to a summer's day! The allusion, whatever its merit, may have grown thin after four centuries of wear. Why fixate there, when there is a bounty of 153 more sonnets to excavate for language, color, insight, mystery, or just shear awe.
Overwhelming as this is, let's start with: 66, 74, 94, 126, 129, 145, 154.
If your favorite is not listed here, and you are prepared to passionately argue about it, I'm willing to make amends.
You may find the sonnets online here:
PS. We'll be meeting in front of Crema at 6pm, then head over to the Radcliffe Yard, where we'll have the reading and discussion. If you can, please have the text of the sonnets with you.