Schottky diodes have no reverse recovery charge so would be a slight improvement if there is a chance the coil would be turned on again before the current fully decays, more common with things like a stepper motor coil than a relay or solenoid. That's my only guess as to what the L298 literature is getting at. Also, the Schottky diode would have lower power dissipation given its lower forward voltage, so maybe that's another thing they're aiming at.
Neither of the above sound relevant for a solenoid application, and a good old 1N4004 (or cousin) should be just fine.
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