The Lenovo ThinkPad X250 has an SSD storage medium which is better than most similar spec laptops that have been around for more than a year. Most laptops that have been available for a similar time to it have an HDD storage medium. Solid State Drives (SSD) store data in semiconductors on a circuit board rather than using magnetic or optical media. Solid State Drives have no moving parts which makes them very fast and reliable.
An SSD storage medium is actually the best storage medium across all laptops of a comparable type and age to the ThinkPad X250.
The worst storage medium across comparable types of portable PC is HDD.
There are a number of other laptops that have an SSD storage media currently available which you might also want to look at including cheaper portable PCs such as the Latitude 12 5000, or the Latitude 12 5000 both from DELL or the Asus UX301LA.
If you would prefer a notebook PC with a better storage medium then you might want to look at the HP EliteBook 850 G2 (SSD).