Formal:
* Consider: Implies careful thought and evaluation.
* Judge: Suggests a more formal and objective assessment.
* Hold: Indicates a strong belief or opinion.
* Estimate: Implies a less precise judgment based on available information.
* Conclude: Emphasizes the outcome of a process of reasoning.
* Determine: Suggests a definitive and final decision.
* Declare: implies a public and official pronouncement.
Informal:
* Think: A general and neutral term for forming an opinion.
* Believe: Suggests a strong personal conviction.
* Feel: Emphasizes a personal and subjective opinion.
* See: Implies an understanding or realization.
* Figure: A colloquial term for understanding or deciding.
* Assume: Implies a belief based on incomplete information.
Other options:
* Find: Indicates a discovery or realization.
* Recognize: Suggests an acknowledgment or identification.
* Accept: Implies agreement with a decision.
* Approve: Indicates a positive judgment.
The best synonym will depend on the specific context and the desired tone of your writing.