Stelios wrote:
1) Best ear for music (perfect/relative pitch)
That one's IMO nearly impossible to know as we haven't got enough information and/or access to controlled experiments to put them against each other in that department (e.g., aural tests to see if they can hear a melody and accurately replicate it either vocally or instrumentally on first attempt).
Stelios wrote:
2) More complex/original ability in composing
They're both different areas, again, and again, there's no way to know for sure. Of course, there's Black Queen and Bo Rhap and Waltz and My Fairy King, etc., but Brian also could do things that Freddie couldn't, and probably John and Roger as well.
In terms of having more chords, modulations, more advanced compositional vocabulary, etc., then yes, Freddie wins. In terms of the craftsmanship of arrangements, all four had different styles and they were all valuable in their own way. Freddie probably wouldn't have been able to arrange '39 or Good Company just like Brian wouldn't have been able to arrange Bo Rhap (vocally) or Seaside Rendezvous.
Stelios wrote:
3) Efficiency on musical instrument/s
Indeed, it depends on whether you count the voice as an instrument. If so, then IMO Freddie was the most advanced. Otherwise, yeah, Brian. I think Brian's ability as a guitarist far surpasses Freddie's as a pianist... in fact, Brian's ability as a pianist and singer far surpasses Freddie's as a guitarist as well.
Now, if we're gonna count their overall ability on different instruments, then perhaps John Deacon was the most advanced one (vocals notwithstanding). He was really good on bass and he was also quite good on guitar (certainly better, IMO, than Brian was on piano or Roger/Freddie on guitar).
I read one of the replies saying that Rog was the only one who could record an album by himself ... well, yes and no... FIS has the late great David Richards playing half of the keyboards, SF has several cameos by Queen members and also some rhythm guitar by Rick Parfitt (and probably again David Richards on keys) and the rest of his albums (including Fun on Earth) have guest musicians.
Roger's ability on synths and piano, at least in the 80's, weren't too much greater than Brian's on bass or drum machines. If we rule out their main instrument, I think Brian's better on piano than Roger on guitar, and he's better on bass as well. The difference between Brian and John would've been that Brian could also sing both lead and harmonies, getting him closer to the whole idea of recording all by himself.
Stelios wrote:
4) "The Harmonies Department" (Queen's trademark)
Depends on what you mean... arranging harmonies, singing them or producing them? Those are three entirely different sets of skills again.
Arranging them - Again, Fred could do things Brian couldn't and vice-versa.
Singing them - Lord Frederick, Earl of Mercury, FTW, with Roger as second IMO. Range-wise, performance-wise, subtlety-wise, etc. Of course, they sounded at their best when they were together (e.g., STL), but all in all I think harmonies sounded better when they were all Freddie (e.g., 'Love of My Life') than when they were all Roger (e.g., 'Tenement Funster') or all Brian ('Leaving Home Ain't Easy'). 'All Dead, All Dead' is a great example of a song where Freddie 'only' sang BV's, but he made the most out of a supporting role and elevated the piece to a whole new level.
Producing them? I'd chose Freddie as well. He had a very nice way to mix them and get them to work. The others did too, of course, but not quite at the same level IMO.
Stelios wrote:
5) Former training in music ( though this can be at odds with actual inherent musical talent)
Both Freddie and Brian got to Grade IV on piano, and that's all the formal training any Queen member ever had.