I voted for Undaunted because I have many cards from that set and my only Legend card is the bottom half of Rayquaza/Deoxys. I have almost all of the initial rare cards and one of my three Primes is from Undaunted.
I also voted for Call of Legends because it has a lot of rare legendary Pokémon cards and the animations for all of them are really good, especially for the shinies.
POP Series 1 also got a vote because it's the only POP Series that I have almost completed.
My own votes go to HS Undaunted because of Raichu Prime, POP Series 5 because of the two gold star Eeeveelutions that are worth quite a bit, and HGSS because of Typhlosion Prime and because it was the first set with the delicious HGSS card style.
Just 2 more days to vote and we're at a 3 way deadlock!
My votes this week go to HS Unleashed and HS Undaunted. Both of them have some of my favorite Pokemon Prime cards from this era, including the Lanturn from Unleashed and the Umbreon from Undaunted, which are easily two of my top 10 favorite card arts of all time.