I'll confuse the matter and say I tend to prefer the left side, as you get to see the neighbor islands. Maunas Loa and Kea are great, as is Haleakala, and if you're really lucky the cliffs of Molokai are quite spectacular, as it seeing Lanai and Kahoolawe lined up. BUT (and this is a big but) you have to have a clear day.

So what was mentioned before about the Oahu sites on the approach from the right side (and add the Koolaus and Hanuama Bay to that) probably makes for a safer bet. Have taken some good photos before from that side.