The Nano X and Nano S Plus are Ledger's entry and mid-range devices. They share the same security, but differ in connectivity and convenience.
The Nano X has Bluetooth and a built-in battery, so it works with phones without a cable. The Nano S Plus is wired-only, which keeps it cheaper and simpler.
The Nano X holds up to 100 apps, while the Nano S Plus holds around 100 apps as well but with a smaller memory budget in practice. Both cover all major coins easily.
The Nano S Plus is significantly cheaper. If you only use a desktop and want the best value, it is hard to beat. If you want mobile use, the Nano X is worth the extra cost.
Desktop users should buy the Nano S Plus. Anyone who wants to manage crypto from their phone should get the Nano X.