Still a lot of variables, and you haven't really talked about what it is you are wanting to listen to.
Getting 25 miles from a hand held scanner is more about what they are listening to than just the antenna they have on their scanner.
If the transmitter is up high with a good antenna, then a paperclip stuck in the antenna jack on your scanner might work well. If it's down low, the limiting factor becomes the curvature of the earth, buildings, topology, etc. No amount of antenna will necessarily overcome that.
If you are trying to listen to VHF and/or UHF stuff, then the antenna you have is probably a good choice. On hand held scanners, the issue becomes how big an antenna the connector can support. At lower frequencies, the lack of suitable ground plane can be an issue.
And, location is key. Comparing your reception to someone else leaves open too many variables to make an accurate comparison.