meeting or to meet?

Grammar accepts both in flipping phrasing. Communication is imaging and focus and the first puts more emphasis on "pleasure" and the second on "meeting you". A better example is the small difference between:

Baseball is my favorite pastime. 

My favorite pastime is baseball.

These strictly are the same communication and if I remember correctly is subject and object forms (Don't punish me if not quite correct in terms.)

The first pictures "baseball" first and second is "pastime".

In communicating, "Meeting you" is more interactive personal, your second choice, as putting the other person ahead of yourself. This is something only noticed by studying the difference in communication.

"Meeting" is a longer period of time implied than "to meet" as a form of communication. In formal business writing, "to meet" is considered better as we often separate personal and business. We have a meeting, which occurs in a time period. "Meet" can be brief.

The form of "To meet you at the conference was a pleasure this month." is an awkward form that technically says the same thing. 

It was a pleasure to meet you at the _____ Conference. 

We delete the "this month" as unnecessary, and it is better to title the name of the conference.

It was a pleasure to meet you at the Child Development Conference.

'Meeting you at...' is the better of those two forms. The other form is ok.

It might be hard to justify grammatically why 'meeting' is correct, and 'to meet' is not, but that is generally how we do it in normal British English in speech. 

In writing it would be fine to have 'to meet' in the middle of a sentence, but not at the start of a sentence - that would feel awkward.