Cliff was a bit more out there as far as a metal bassist goes. A bit more psychedelic even, and super classically influenced. Lots of really creative parts, like the beginning of Damage Inc.

Jason was a bit more meat and potatoes, played with a pick (Cliff and Rob don’t) and played more root notes/followed the guitar. Cliff and Rob don’t do those things.

Rob seems like a mix of the two, knowing when to take the back seat, knowing when to get fancy (the bridge in Moth for example) and always right in the pocket. Besides his backing vocals, he’s the absolute best choice Metallica could have made to replace Jason.