Summary
Werewolves are always a fun concept. A hidden monster between people, waiting to unleash its bloodthirst on whoever is unlucky enough to be on its way, where the victim of the curse can find a way to get rid of it, learn to control it, or submit to it.
Dungeons & Dragonshas adapted these creatures to fight against or even allow players to become one, but it has also made quite a few variations using other animals. Some even work in a different way, where the person doesn’t necessarily turn evil or have full control of the transformation. And while even the weakest ones are already fantastic enemies, which are the best to use in a game?

7Werewolf
Perfect To Introduce The Concept Of Lycanthropy
The basic lycanthrope is still one of the best to use when your game isat a low level. Their attacks are simple but strong enough to be quite a challenge, as well as a good way to introduce the standard damage immunity that comes with all lycanthropes - the immunity from any slashing, bludgeoning, and piercing weapon that isn’t magical or silvered.
It’s important to note that they won’t be as powerful if your party begins to reach higher levels, but it’s also easy to give werewolf features to another creature to make them a werewolf themselves. What would happen if a Gladiator NPC was bit by a werewolf, for instance? Though you can do it with other lycanthropes, too, werewolves' simplicity is what helps you here.

6Jackalwere
Reverse Lycanthropy
Though this is by far the weakest option here, that only makes them even more interesting for low-level campaigns, especially because they still have powerful damage immunity despite their low AC (Armor Class) and health. They also come with the fun little twist of being regular animals who were transformed rather than the regular lycanthropy - Sadly, that means they don’t turn into people, so there is nomystery behind who’s the monster.
Despite being squishy, they come with exciting features. Not only do they have Pack Tactics, meaning a group can be lethal, but they can also use weapons while transformed and have a Sleeping Gaze, which forces the target into a Saving Throw and will force them to sleep if they fail. Two of these guys fighting side by side can be a big enough threat to a first-level group.

5Wererat
They Come In Different Sizes
Wererats are one more contestant for a low-level campaign, but they have a significant change that makes them interesting: While they can also use weapons like the Jackalwere, their basic weapon choices consist of hand crossbows, meaning they can be a challenge from afar.
They also have two official variations mixing two specific species: Halflings and Svirfneblin (Deep Gnomes). These are Wererat stats that mix some of the species' innate features, such as the Halfling’s resistance to being frightened or the innate spellcasting of Gnomes (rules as written; they can’t cast while transformed due to the verbal component, but you can change that, DM).

4Werebear
The Damage Sponge
If your players are a bit stronger by now, you should consider throwing a Werebear on their way. They are good aligned, which means they aren’t necessarily aggressive, but that’s up to you. They have a lot of health to accompany their immunity and a great axe to cause more damage than normal.
They also havea Goliath variation,with more health, cold resistance (though fire vulnerability), and Goliath’s Stone Endurance reaction, allowing them to decrease the damage they’ll take. This variation’s CR increases to eight, and they can be formidable opponents.

3Wereboar
Lycanthrope’s Barbarian
Though slightly weaker than the bear, the wereboar is a formidable opponent, and its alignment makes it more aggressive, too. Along with a maul, it can charge towards an opponent, potentially making them prone depending on the Saving Throw result.
It also has a unique feature called Relentless, meaning that when it takes an attack that causes 14 damage or less, and this attack makes its health reach zero, it’ll instead stay up with one hit point. The wereboar can only use it once per short rest, but it’s still an efficient way to stay in combat for a little longer.

2Werevulture
The Best Of Everything
Unlike the other options here, Werevultures don’t possess the damage immunity most lycanthropes are famous for. While that is a considerable nerf, it has its own features that make it interesting.
First, it has Regeneration, recovering ten hit points at the start of its turn, similar to vampires. It can also wield weapons, including a longbow, and it can transform with its bonus action, meaning it can change forms and still attack. Their beak attacks activate the curse, and if they zero someone’s health after they’re cursed, you can immediately turn the victim into another werevulture.

Last but certainly not least, they fly, and airborne enemies who can use ranged weapons are a fun challenge for the players.
1Redtooth Werefox
With a Whole New Concept
The werefox has a whole unique concept in terms of roleplay: They are a specific group of Elves from a place called Redtooth Keep who were cursed, and this curse isn’t contagious through bite, meaning only these Elves have the transformation. You can change that, of course, but it’s good to know nonetheless.
They don’t have special immunity or regeneration, so they keep up with others by being deadly combatants. They can also charge the enemy to knock them prone and have access to long-range weapons that can potentially restrain the opponent depending on the Saving Throw. Their transformation can also happen with a bonus action. Finally, they can dash and disengage with their bonus action, too, which makes them quick creatures - especially since their movement is 40ft.