G3 definitely did the holiday ponies the best, none of the G1 ones really stand out to me.
My favorites are:
Valentine-Candy Heart
Easter-Lolligiggle for sentimental value, but Rainbow Sunrise has my favorite design overall
Halloween-Pumpkin Tart, honorable mention to HQG1C Batty Boo
Christmas-Snowflake, honorable mention to HQG1C Dasher