The geography first, because it explains everything else. The Nile flows north, so a boat sailing from Luxor to Aswan is heading upstream — south, against the current — and the return direction rides the flow. The classic circuit between the two cities is the same either way: through the lock at Esna, then calls at the temple towns of Edfu and Kom Ombo — the latter on its bend in the river. Nothing on the itinerary changes except its order.
What changes is the dramaturgy. Sail south and the trip is a crescendo: Luxor's enormous temples first, then the river narrowing and emptying, then Aswan — granite islands, dunes, Nubian villages — as the finale, with Abu Simbel sitting beyond it as the optional encore. Sail north and you open with Aswan's calm and finish among Luxor's giants, walking into Karnak with your river legs already on.
How to actually decide
Let the flights choose. The cruise fixes which city starts your Upper Egypt leg, and the smoothest itineraries fly into one city and out of the other rather than backtracking. If your Cairo days come first and the connection lands you in Aswan, the decision has been made for you — and it is a good one.
If the flights are flexible, choose by temperament. Savers of the best for last should sail south and let Aswan close the show. Travellers who want the hardest sightseeing done early — Karnak and the west bank ask the most of your legs — should also note that the southbound run typically takes an extra night, which is a gift, not a cost: more deck, same temples.
Our 4-night Luxor to Aswan cruise is the southbound shape; the 3-night cruise runs the faster northbound version. The full fleet, in both directions, is on the Nile cruises page.
The one myth to drop
There is no 'better scenery' direction — it is the same riverbank at the same walking pace, and boats do the bulk of their sailing in daylight either way. Anyone selling one direction as the scenic one is selling the cabin they have left. The honest differences are order, pacing and flights; on those, either answer can be right.