When raising a ticket, it is important to understand what the priorities mean specifically for each value. Here is a guide to help you decide which priority to use.
Urgent!
This is to be used (sparingly) for business critical issues only. This level of priority is a request for the issue to be resolved as soon as possible as it is effectively stopping that part of the business and there are people waiting on the resolution in order to continue. We will drop everything in order to solve this ticket.
Resolution Time: ASAP, depending on solution but will be looked at straight away.
High
This is an issue that is of a serious nature and needs to be resolved within 3-4 hours but it is not stopping the person from continuing from their tasks.
Resolution Time - Within 4 hours.
Medium
This is an issue that is not business critical but will need to be resolved within 24 hours. We will always do our upmost to solve tickets as soon as we can.
Resolution Time - Within 24 hours.
Low
This is a low severity issue that is not business critical and can be looked out within reasonably time. This will be resolved with 3 days but we will always do our upmost to solve tickets as soon as we can.
Resolution Time - Within 3 days.
Final Note - My personal experience of using priorities is to think of high and urgent levels as tokens for which you have a certain number. If you always use Urgent then how can anything be more serious and the likelihood is that it will not be taken as that and be downgraded.