how does soundcloud's own compression/streaming algorithms affect the sound?

I prefer # 3 overall, with #6 a close second

Another vote for #3. #6 would be my 2nd preference although the vocal is a touch sibilant for my taste. In #1 & #5 you can really hear the limiter working.

Soundwise

hueseph
if you had taken the time to match volumes you would have found that the transients were in fact more prominent in 2 and 4.

You can tell that just by looking at waveforms as well.

Exactly.     
 
I was listening on headphones, at work.  Level matching simply wasn't an option....    However, it was a real-world/outside the studio listening experience, as 99% of the target audience is likely to do.   
 

Great idea ! I have listened to each track in sequence, making notes as I listened on notebook. I listened back one more time to verify my notes. Here they are copied and pasted below....
 
 
 
Premaster. Strings not jumping out. Vocals clear. Bass indistinct. Snare could sound 'better' Kick drum and bass dull together.
1. Mastering Blind Test #1. Guitar brighter - louder so took level down. Bass guitar more resonant, as are toms on kit. Less dynamics, brighter.
2. More mids. Guitar less bright. Kick more punchy. Feels more 'cohesive' I like because its subtle.
3. Hotter (like 1) Good dynamics. Snare really snaps. More aware of hi-hats so more toppy.
4. Softer mastering, cohesive. Perhaps a little too subtle? Not coming full on at me on my studio monitors (KRK Rokit 5's) what do I mean? not punchy enough? My least favourite so far.
5. Least subtle so far. Seems missing some 'body' A little toppy. The missing 'body' returns in the chorus, but a little boomy. Easy to like at one level, but could be ear fatiguing after a couple of plays.
6. Nice kick drum. Snare not as prominant but doesnt take away from the feel. Best tone on the sidestick. Melds together well. Not 'boomy'.
 
 
My favourites. 2 and 6. For different reasons. 2 is subtle but very 'glued' together sonically. 6 is punchy and in your face but everything balanced. My least favourite, 4 and 5, 4 a little 'dead' and 5 too ear fatiguing possibly.
 

 
 
I'm not that au fait with Soundcloud, so could someone please tell me how to download the various versions.
 
Also, are we listening/downloading .wav quality files, or making mastering judgements on 128kbps mp3s?
 
 

That's why I asked that the files be made downloadable, which CW says is not possible due to copyright constraints. You're right, we're judging masters based on 128 kb/s MP3s, which might be a legitimate test if we assume the song has been mastered expressly for online streaming. SoundCloud does not, AFAIK, add any compression, though.

It seemed to me that #2 and #4 were so similar that any perceived differences might be imaginary. So I downloaded them both and loaded them into Audition for an objective analysis (just measuring the first verse).
 
Sure enough, they were so close that I even began to wonder if Joey might have played a trick on us. The measured differences are well below anything that would be audible, whether looking at average RMS, total RMS, min/max RMS, peak amplitude, min/max sample values, level distribution or frequency spectrum.
 

Thanks for the clarification Dave.

 
I just noticed that the vocal is a lot harsher at the end of the song than the beginning (hadn't listened all the way through before).  I much prefer the first part of the song.