It was the most fabulous wedding reception that I have (or had) ever attended.
It is the most fabulous wedding reception that
I have ever attended.
It was the most fabulous wedding reception that
I had ever attended.
As you can see, the trick with this construction is to move the second half of the sentence two tenses further into the past than the first half.
First half: present tense = Second half: present perfect
First half: past simple = Second half: past perfect