For a general claim:
* Assertive: This implies a strong and confident statement.
* Declarative: This emphasizes the statement's nature of declaring something.
* Stated: This is neutral and simply indicates that something has been said.
* Alleged: This implies that the claim is not yet proven or verified.
For a specific type of claim:
* Speculative: This indicates a claim based on conjecture or guesswork.
* Controversial: This implies a claim that is likely to cause disagreement.
* Unfounded: This describes a claim that lacks evidence or justification.
* Dubious: This implies a claim that is questionable or suspect.
* Valid: This describes a claim that is justified and accurate.
Other related words:
* Claimant: The person making the claim.
* Claimable: Something that can be claimed.
Ultimately, the best adjective to use depends on the specific context of your sentence.