Inquiry is the more common and preferred spelling in American English.
Enquiry is the more common and preferred spelling in British English.
In practice, both spellings are considered acceptable in both regions. However, using the spelling that aligns with the regional dialect is generally considered more appropriate.
Here's a quick table to summarize:
| Spelling | Region |
|---|---|
| Inquiry | American English |
| Enquiry | British English |
You can use either spelling without worrying about being grammatically incorrect. Just be mindful of your target audience and the context.