I should state the obvious here, which is that it has been discussed a number of times, so it'd be worth searching for previous responses.

If it's a one-off type experience, a longer flight certainly makes more sense (SIN, GIG, CPT etc).

The A380 used to be recommended on the basis of the tasting menu but I believe that has now been dropped?

787 has the most modern IFE and should generally be in the best condition (in theory).

Routes with 2/3 aircraft types would allow you to try a couple out.

747 is less popular but being in the nose/1AK is a 'must try once' experience.

But travelling to somewhere you wish to visit/that you can find redemptions for is the best answer as always.