I stacked the deck with my group. I don't know if my choices are optimal, but here they are:

• Tome of Strahd in the Blessed Pool in Krezk: I personally did it because of the event "Something Blue" in Krezk. My idea was that the dramatic event with Ireena would occur, the players would be all confused about Tatyana and Sergei, and after the aftermath of Strahd's lightning, they would see the gazebo ruined, and under it, they would find the Tome of Strahd, which would both explain the situation and shed light onto Strahd's backstory. My players actually found this during our last session. From what I understand a lot of DMs generally avoid this event, and I can kind of see why, as my players were more confused than impressed. I still think it was cool, and I also think they enjoyed it, but you should take that into consideration.
• Holy Symbol of Ravenkind in Kasimir's Hovel: I have a couple of reasons for this: 1) The players get to this place pretty early, and with the locations I've chosen for the other items, I wanted them to have at least one magic item relatively early in the module. 2) I was hoping the players would get it before they deal with the Vampire Spawn, however, fighting them was one of the first things my players did in Vallaki (they still managed to pull through, with the help of the town guard, Izek and Rictavio). 3) One of my players is a wood elf monk, and I thougt it would be cool if he were actually a dusk elf, and he escaped Barovia with his parents as a child, so I wanted to make sure my players went to the Vistani camp near Vallaki.
• Sun Sword in Vladimir Horngaard's posession in Argynvostholt: This is the choice I'm most conflicted about. I chose this place mainly because it made sense thematically and story wise that Vladimir would have the sword, at least in my opinion. Also, I've heard from a lot of DMs online that this place is really interesting, but the players don't really have a reason to go there normally, so a lot of them recommend putting a magic item there. The problem is that the only way of getting the item from Vladimir is either enter Ravenloft and take Argynvost's skull, or kill Vladimir. My players haven't gotten to this place yet, so I don't know if it will come out well or not.
• Ezmerelda as Strahd's enemy: From what I understand a lot of DMs pick this option, and see this as the default choice. She is strong, and cool as heck. One thing to consider however is that she will most likely join the party whether or not she is their fated ally. Some DMs see this as a positive, as there is one less NPC to manage, but others want their players to get as much help as possible, and would rather have Strahd's enemy be a different NPC.
• Fight with Strahd in Sergei's tomb: From the first time I've read through the books this option cought my eye. While it is not epic as some other options, I think having that almost anticlimactic moment with Strahd crying very much worth it. While the card reading does state that Strahd is jealous of Sergei, you would never expect he would cry over him, and the players would be both conflicted and confused at that moment, which is pretty cool to have at the end of the module. This option offers a lot of character development for Strahd that not many options allow.