I'm an aisle flyer, but I'll make an exception for KL's daytime flights to NBO, JRO, JNB and CPT. Those are the only ones where I try to get a window seat.
I can't quite decide which is my favorite, but it is probably JNB.
On flights to JRO and NBO there is a good chance that the aircraft will fly along the eastern bank of the Nile for quite some distance, at least as far as Khartoum, sometimes further. This makes for spectacular sunsets, with the river gleaming in the foreground and the Sahara stretching to the horizon in the background.
JNB flights normally cross into Africa near Tripoli, and then continue in a straight line, heading almost due south to a waypoint at SEB (Sebha), an airfield and oasis in the in the absolute middle of the Saharan nowhere, but nevertheless surrounded by a surprising number of cultivated fields. The plane then changes course to the south-southeast, and an hour or so later flies right over the Tibesti Massif (those "giant mountains rising out of nowhere") in northwestern Chad. Some of the mountains are quite precipitous, with the highest peak rising to over 3.400 meters. Flying past at an altitude of 9 or 10 km, the mountains thrust straight up at the aircraft, with every detail standing out in the often crystal clear air. Eons of torrential rainfall have gouged out canyons and rivers valleys. The trees and shrubs lining the latter in places can be seen with the naked eye, even from 30,000 ft (as, by the way, can cars driving along the very few roads in the Sahara). On one occasion I was even treated to a couple of storms raining down water on the mountains.
The Sahara itself I also find fascinating. Apart from the never-ending sands, which come in an infinite range of hues and colors, the rock formations add variety and interest.
The transition from Sahara via Sahel to tropical rain forest comes just before sunset, and depending on where the inter-tropical conversion zone is hanging out, some spectacular thunderstorms may provide extra entertainment (at this time of year the ITCZ should be close to the equator)
On top of all this, the European part of the flight almost always offers fantastic views of the Alps. The exact flight path over Europe varies, but sometimes the plane follows the Rhine through Holland and Germany, on occasion almost far as Basel in Switzerland.
Crossing the Mediterranean will afford views of Sicily, and sometimes Sardinia and/or Corsica as well.
All in all these flights never bore me, I can spend hours with my nose glued to the window, no matter what side I'm seated on!
Johan