It shouldn't be better than bluetooth, but there are other factors that could influence the sound quality. Bluetooth connection stays digital until it reaches the BT speakers where it does the DAC. The 3.5 jack route does the DAC in the MBP, then there are more variables that could affect the sound quality after that, namely the cable itself, the analog connections. I suppose it's possible for the analog route to be better if the DAC in the MBP is significantly better than the one in the speaker. Also there could be connection issues in the BT that affect the sound, but those are rather obvious, drops, skips, etc. Are you talking about using the same speaker that has both BT capability and analog jack? All things being equal, the BT should sound better because of the lower chance of analog interference and variables, assuming the DAC's are close in quality.
You're a funny dude, but I'll bite. Content, youtube or anything else will not matter on which has better relative sound. The relevant facts are what was stated above: which BT speaker, analog cable used, distance, any other sources of potential interference, any other connected hardware in your setup. Without knowing any specifics, it's hard to say. But I'll assume you're using a regular BT speaker and not anything on the high end audio level that @ZapNZs is talking about. In that case, BT should sound better by transferring as much info digitally without analog loss. I've experienced this in various setups, specific sounds that weren't audible before through analog. That being said, if you have any drops in connection or interference, BT will clearly suck more. But regular BT setups should sound better, if you can distinguish the differences at all. The quality of the speakers, and to a lesser degree the amp if applicable, will really dictate whether you can hear differences. TLDR: it shouldn't be much different in either case with the same consumer grade BT speaker.
