Lord Howe Island or Norfolk Island? It's a tough call even for me, having been to both islands. Both are magical, beautiful, and remote outposts of Australia. Darcelle says that's where the similarities end. Those who've been to one or the other might presume one is just like the other but there are actually more differences than similarities.
Both islands are upmarket destinations catering to two different crowds. Norfolk attracts retired couples whereas Lord Howe attracts mostly families and honeymooners. Tourism is the main industry on both islands yet Norfolk is more commercialized. With an approximately 7:1 ratio of cars to residents on Norfolk, nearly everybody hires a car and nearly every resident owns at least two vehicles. On Lord Howe, you can count the number of hire cars on one hand and nearly every visitor hires a pushbike. Furthermore, residents can't buy a car if they already own one (unless they have their old one shipped off the island). Lord Howe lacks the deep and dark history of Norfolk as there has never been a convict settlement. Travellers visit Lord Howe more for its outdoor activities and nature than for its museums and history.
Sharing is second nature on both islands and helping out your friends and neighbours makes a big difference. It's a fact of life to babysit others' children, have communal dinners, and ask friends/family flying in from the mainland to bring some fresh strawberries or your favourite bottle of wine.
On Norfolk I've heard many great things about Lord Howe and assumed most Norfolk Islanders have family on Lord Howe, but there's a rather small connection to the mutiny here on Lord Howe. There is no Bounty Day or Thanksgiving here and little to celebrate the history of the Pitcainers. For all intents and purposes, Lord Howe has always been part of New South Wales. Aside from Darcelle, Willow, Nobbs, and their immediate family there are no other Norfolk- or Pitcairn-Islanders living on Lord Howe.
On Google Earth, Norfolk looks somewhat like a shriveled-up prune yet is relatively flat compared to Lord Howe. Mt. Bates is only 319 metres at its highest point. Lord Howe is shaped like a banana and is much more geographically dramatic than Norfolk. Mt. Gower (875 metres) and Mt. Lidgbird (777 metres) soar like needles above the ocean with a very high relief.
Lord Howe Island and Norfolk Island: somewhat similar yet a world apart and very different. One is a sexy blonde, the other is an attractive brunette, yet they're stunning enough that, in the travel world, you'd easily find them both on the catwalk.