Both options Via the Internet will sound the same. An ACTUAL VINYL RECORDING WILL SOUND BETTER. The difference being that it hasn't been digitally converted to a sample rate i.e. 44.1k 16 bit which is CD quality. The reason why Vinyl will always sound better is because of the sample rate, which if the Vinyl was cut earlier than digital recording will remain in tact. Making analog recordings infinitely more precise and accurate as opposed to digital audio. (this has to do with analog magnetic tape as opposed to hard drives and digital audio)
Therefor, Youtube vs another digital copy of audio more than likely won't have much of a difference. The sample rate on the digital copy might be higher, like 48k 24 bit. Altogether, the difference in digital audio can be very hard to hear. For the record, i would always suggest using 48k 24 bit for the sake of being able to size down if required. You always want to hear you mixes as HQ as possible! (There are higher sample rates and bit depths available, but not all Digital Audio Converters can operate under them. the mbox mini can only go to 48k!)
Your solution? Record your samples into a DAW that can record at HQ sample rates (higher than 44.1k 16 bit) because you can always back track on the quality of the sound if you need to. you can't ADD quality to a recording.
Finally, if its an mp3 you're basically shooting yourself in the foot for an unimaginable amount of reasons. Don't. Use. Them. unless of course, you have to.
This is from my stand point. In terms of a project studio, just for fun, or even just simple usage of audio it really isn't a big deal. A regular non critical person wouldn't be able to tell the difference, so its all personal preference my man. Choose wisely!