Of you are gonna get long bands then you may as well just use em for everything. You can double up a long band, but you cant make a short band longer. Although i will say if i get to choose, i still prefer short bands for bench and deads, its just slightly less hassle.
Also it depends on your setup, for instance one of my gyms has squat racks i can do reverse band squats and deads with the bands on the pins. If your only option for squats is looking for pegs on/near the ground, or using DBs, then obviusly you have no choice.
And finally, they arent super expensive. Grab a couple of each and try em out.