I voted JPJ even though I own a bass that was custom made for, owned and played by Entwistle. JPJ on Zep 2 does one of the best jobs at perfectly blending driving bass riffs in with the rest of the band without over powering or under delivering. Entwistle on the other hand had a very unique style that filled a lot of sonic space but always seemed too busy and note rich to me. Actually of all Entwistle's music I think I like his Alembic days best as opposed to his thunderbird days.
I enjoy bass lines most when they are fundamental, supportive, solid and relatively simple. But heck, I'd carry water for either of these guys all day long. Two of the best.