Neither works. For good samples, you need many samples to cover the whole range.
A sample that is too low will have a really short decay when high pitched and thus sounds unnatural.
A sample that is too high, sounds very sluggish on a low frequency, but it will sound better than the other way around, just not in every case. For example, a strings will work if you have a high pitched sample, and play it down on a low octave. But a trumpet will simply sound bad if its too far off its pitch.
Although a guitar has the properties of a string and thus the high pitched sound sounds okay-ish on a low octave, because it is a pluck instrument, that pluck just sounds unnatural.
But there are plenty of instruments that give you a good quality sound. Also, don't forget VST Instruments. They sometimes use syntheses to combat requiring lots of gigs of samples to create a good sounding orchestral instrument. They basically have the beginning part recorded as sample, and sustain the loop. Not the most realistic way, but usually sounds great. The same can be achieved in a Sound Font (.sf2 and .sbk) which can be played using a Sound Font player VSTi. And there are loads of instruments you can download for free in the .sf2 format.