If stocking up for any long term emergency, whether simply a blackout or something more serious, cost can be a consideration if large stocks are required.
It should be noted that AAA cells cost about the same as AA but contain only about the half the energy. The reduced weight may make the cost penalty acceptable for long distance backpacking, but not perhaps for home use.
D cells contain about 8 times the energy of AA for only about twice the price.
I would therefore allways prefer D cell flashlights, lanterns, and other appliances for longer term use.
The humble D cell Maglite gives 12 hours good light on Alkaline cells, this may be greatly extended by fitting a lower powered incandescent bulb or an LED.
Remember that in an emergency popular batteries may be unobtainable, but the more obscure ones might still be available.
Therefore IMHO prudent preps should not only include qaulity flashlights to take your prefered battery, but also some cheap lights for every type of battery you can think of!
I have flashlights or lanterns to take
AAA, AA, C, D, CR123, PJ996, AD28, and others.

Remember also that in some climates, heat can kill, not just cold, anywhere warm a couple of battery fans would be a prudent prep. I believe that these can be purchased in the USA but here in the UK I made my own. Run time is about 24 hours on 6D cells.

I also made some D cell LED lights that run for 1,000 hours on 3 D cells, these are not that bright but enough for safe movememt.
A case of 50 D cells would provide basic essiential lighting for 10 years with these LED lights.