Judging by Amazon Sales Rank, the most often sold rulebooks published officially by WotC after the three core books are, in order:

1. Mordenkainen presents: Monsters of the Multiverse
2. Tasha's Cauldron of Everything
3. Xanathar's Guide to Everything

There also is a Gift Calendar, a Core Rulebooks Gift Set and an Essentials Starter kit in the top ranks, but from your question, you already have the core books, and are looking for books only, in particular rule books, not for Kits or Gift Sets.

Monsters of the multiverse has been published last, and will mostly be useful to a DM, although as a player you might be able to use the race options with your DM's OK. Other than that, as a player, you won't need it: reading up on the monsters in advance can cost you the suspense of discovering their abilities through play and make it harder to role play your character, who most likely knows nothing about them. For a DM the wider monster selection is quite useful when writing own adventures. If you play with pre-published adventures, they either use Monster Manual monsters or include statistics for other new monsters they use, so you won't need it for that.

The other two both contain DM-facing material and optional additional feats, subclasses and even classes like the Artificer in Tasha's, so they are useful for both player and DM (just note it is all optional, so you need your DMs OK to use any of it). Tasha's is the newer of the two.

Judging by Amazon Sales Rank, the most often sold rulebooks published officially by WotC after the three core books are, in order:

1. Mordenkainen presents: Monsters of the Multiverse
2. Tasha's Cauldron of Everything
3. Xanathar's Guide to Everything

There also is a Gift Calendar, a Core Rulebooks Gift Set and an Essentials Starter kit in the top ranks, but from your question you want to know about books only, in particular rule books, not Kits or Gift Sets.

Monsters of the Multiverse has been published last, and will mostly be useful to a DM, although as a player you might be able to use the race options with your DM's OK. Other than that, as a player, you won't need it: reading up on the monsters in advance can cost you the suspense of discovering their abilities through play and make it harder to role play your character, who most likely knows nothing about them. For a DM the wider monster selection is quite useful when writing own adventures. If you play with pre-published adventures, they either use Monster Manual monsters or include statistics for other new monsters they use, so you won't need it for that.

The other two both contain DM-facing material and optional additional feats, subclasses and even classes like the Artificer in Tasha's, so they are useful for both player and DM (just note it is all optional, so you need your DMs OK to use any of it). Tasha's is the newer of the two.

Judging by Amazon Sales Rank, the most often sold rulebooks published officially by WotC after the three core books are, in order:

1. Mordenkainen presents: Monsters of the Multiverse
2. Tasha's Cauldron of Everything
3. Xanathar's Guide to Everything

There also is a Gift Calendar, a Core Rulebooks Gift Set and an Essentials Starter kit in the top ranks, but from your question, you already have the core books, and are looking for books only, not for Kits or Gift Sets.

Monsters of the multiverse has been published last, and will mostly be useful to a DM, although as a player you might be able to use the race options with your DM's OK. Other than that, as a player, you won't need it: reading up on the monsters in advance can cost you the suspense of discovering their abilities through play and make it harder to role play your character, who most likely knows nothing about them.

The other two both contain DM-facing material and optional additional feats, subclasses and even classes like the Artificer in Tasha's, so they are useful for both player and DM (just note it is all optional, so you need your DMs OK to use any of it). Tasha's is the newer of the two.

Judging by Amazon Sales Rank, the most often sold rulebooks published officially by WotC after the three core books are, in order:

1. Mordenkainen presents: Monsters of the Multiverse
2. Tasha's Cauldron of Everything
3. Xanathar's Guide to Everything

There also is a Gift Calendar, a Core Rulebooks Gift Set and an Essentials Starter kit in the top ranks, but from your question, you already have the core books, and are looking for books only, in particular rule books, not for Kits or Gift Sets.

Monsters of the multiverse has been published last, and will mostly be useful to a DM, although as a player you might be able to use the race options with your DM's OK. Other than that, as a player, you won't need it: reading up on the monsters in advance can cost you the suspense of discovering their abilities through play and make it harder to role play your character, who most likely knows nothing about them. For a DM the wider monster selection is quite useful when writing own adventures. If you play with pre-published adventures, they either use Monster Manual monsters or include statistics for other new monsters they use, so you won't need it for that.

The other two both contain DM-facing material and optional additional feats, subclasses and even classes like the Artificer in Tasha's, so they are useful for both player and DM (just note it is all optional, so you need your DMs OK to use any of it). Tasha's is the newer of the two.