sorry, you are wrong(keyboards)

Yes, it's pointless to claim anything conclusive, but it's interesting to read the rationale for the opinions.

Limiting it to prog, to avoid dragging in guys like Bruckner, who could improvise serious fugues on the pipe organ...

Emerson, definitely. Not just as a keyboardist, but as a composer and interpreter. Wakeman himself has praised Emerson's left hand abilities.

Wakeman is very prolific, but the only really compelling stuff I've heard is Six Wives of Henry VIII and his work with Yes. The latter isn't a fair comparison with Emerson, though, because Wakeman has a lot less to do in what often amounts to The Steve Howe Band. I've watched them both in concert, very closely, and the amount of straight filler comping that Wakeman did came as a bit of a surprise. Emerson, on the other hand, well, often has to play independent complex parts with both hands.

Nice to see Jon Tout (Renaissance) and Tony Pagliuca (Le Orme) mentioned. Tout is very underrated (listen to Live at Carnegie Hall), and Pagliuca's synthesizer work on Felona e Sorona was quite innovative.

I would also add Flavio Premoli (PFM) and Le Orme's current keyboardists, Michele Bon and Andrea Bassato. Unfortunately Premoli couldn't make it to Nearfest'05. But the Le Orme guys were there, and it was refreshing to see a band without a lead guitarist. It's almost heretical. Aldo Tagliapietra plays more bass and sitar than guitar, and Bon (on his self-built synthesizer) does a stunning job of imitating a lead guitarist. Bassato is more classically inclined, has a great touch, and contributed a lot of strong contrapuntal writing to Elementi and L'infinito.

Finally, Jurgen Fritz (Triumvirat) and the late Rick van der Linden (Ekseption, Trace).

I play keyboards too.

As I said in other posts, I tend to privilege expression over sheer technique.
Thus, I prefer keyboard players that are able to create a mood and a soundscape, like Tony Banks and Rick Wright.

As regards the two superheros this thread seems to be about, I definitely vote for Wakeman over Emerson, the latter lacking in composition: ok, he's technically gifted and his stage presence is undeniable. But, apart from the pyrotechnics and antics, can you remember any interesting musical phrase he's written? Maybe Aquatarkus or Honourable company...but stuff like The three fates, Iconoclast and the like get easily skipped in my player! A job lot of notes with no sensible relationship...
Wakeman, on the other hand, is capable of conceiving interesting music: this hasn't shown much while he was in Yes, but as a soloist he penned outstanding tracks (for example, The Six Wives, Criminal Record, No Earthly Connection and Out there contain particularly beafutiful tracks). I have to agree, however, with who pointed out the cheesy timbres he uses recently!

The bottom line is...Jon Lord kicks them both in the ass when it comes to technique and expressivity combined, using the Hammond organ or the piano! Man...those breathtaking solos on Highway star, Lazy, Burn and most of all Rat Bat Blue!!!!

Praises also to my fellow countrymen Gianni e Vittorio Nocenzi!!!