Here’s a cheat sheet of their synergy with every current playable character.
Great means that weapon works well with the character, and it’s one of their best weapon options. Decent means that it works on the character, but there are other far better options (usually 4-star weapons). Not recommended means that it doesn’t synergize well with the character – or they have significantly better options (usually craftable weapons or 3-star weapons).
Skyward Atlas
Skyward Atlas is one of the few 5-star catalysts in-game, so it’s one of the best ones… by default. Still, it is a good weapon in its own right. This is thanks to its abundance of ATK and passive that most ATK-scaling DPS catalyst users can benefit from. So it basically works with every ATK-scaling catalyst DPS in-game.
Skyward Blade
Skyward Blade is a relatively useful sword that works best on units that need Energy Recharge (ER). However, it does compete with other 4-star weapons in this role – namely, Favonius Sword and Sacrificial Sword. They’re generally better ER weapons that have more useful passives. There aren’t really any characters that can take full advantage of Skyward Blade, but it’s viable. Because of this, it’s not recommended to actively pull for this weapon. And if you do get it – don’t worry! – it still works on many units.
Skyward Harp
Skyward Harp is the best Skyward Series weapon. It’s basically just a really good bow with a high Base ATK, double CRIT stats, and a very easy-to-proc passive – so it can easily work with every ATK-scaling DPS bow user. It’s also one of the better weapons that can be featured in the limited weapon banner. This means that if one of the two featured weapons is Skyward Harp, it’s definitely one of the better gacha banners in-game.
Skyward Pride
Skyward Pride is a decent weapon that’s only situationally good. And this is in situations where your character needs Energy Recharge (ER) but your artifacts don’t have any ER – or it’s very minimal. For instance, Eula’s ER requirements are around 150-160% ER. So if you don’t have enough ER from her artifacts, Skyward Pride becomes a good option. Is it anyone’s best-in-slot weapon? Not at all – but, hey, it works! So it’s not really useless. Although if you don’t need ER, Skyward Pride does lose some of its value. In this case, there are far better weapon options – some of which are even 4-stars. Because of this, it’s never encouraged to actively pull for this weapon.
Skyward Spine
Skyward Spine is a good polearm in a sea of really good polearms. Basically, it works well on most polearm users but not really the best for any of them. Still, most polearms perform really close to each other. So although Skyward Spine is often a minimal upgrade, it’s definitely still an upgrade.