Which is the greatest piano work composed by Beethoven?

I personall think it's the Opus 53: Piano Sonata No. 21 in C major ("Waldstein").

The "Waldstein" Sonata was the first composition to be written by Beethoven on a bolder and more resonant instrument than any he had previously owned, it had an extended keyboard which allowed for another five notes to be added.
In the "Allegro con brio" Beethoven builds a movement of astonishing richness and nonchalant bravado. The "Adagio molto" forms no more than a bridge between the extended structures of the outer movements and the finale is one of the most sublimely radiant pieces Beethoven ever penned, so that even the brief excursions into minor key territory emerge as positively amiable.
And of course the Sonata op. 106, "Hammerklavier", one of the composer's most important piano sonatas and certainly his most technically demanding. As Beethoven informed his publisher, a sonata which "will give pianists something to think about when they play it fifty years from now". This Sonata does indeed mark the transition from Beethoven麓s middle to late period.

I really like his Moonlight Sonata, but his 9th symphony was also very moving. It's hard for me to choose between the two, I guess it just depends on what mood I'm in.

Moonlight sonata

The third movement from the Moonlight Sonata is breathtakingly brilliant.

Sonata for Piano No. 14, 'Moonlight' in C sharp minor, Op

F眉r ELISE, played in Salterio!!!

For solo piano, my vote goes to Piano Sonata No.23 in F minor, Op.57, "Appassionata."
As far as concertos goes, I'd say Piano Concerto in G major, Op.58.
Which ever one you pick - it is a tough choice... I am also very fond of Piano Sonata No.30 in E major, Op.109.

My favorite is the Second Piano Concerto. It's easier to play - for me any how - than the other four; and somehow, the most rewarding to listen to.

My least favorite by the way, is the Fifth. Something about it that just turns me off.

Wotan

Well, it is NOT Fur Elise or the Moonlight Sonata.

Possibly Hammerklavier

or perhaps the "Emperor Concerto" ; his 5th piano concerto.

WELL THEN Moonlight Sonata C# Minor, Made 1801, published 1802. Made FOR Guillia Gucciardi, that filthy whore WHO DIDNT DESERVE SUCH AN AWESOME LOVE SONG but still. Full of emotion and awesomeness, best love/piano composition EVAAAAR! :) I love you Beethoven. R.I.P
-Ryko

Once again the musical ignoramuses go for the oh-so-predictable Moonlight Sonata and the little minature called 'F眉r Elise'. How on earth can THAT be Beethoven's greatest piano work when compared to the mighty sonatas? Oh, I know - because you never bother listening to anything else, that's why!

I'd plump for the 'Hammerklavier' Sonata - the most challenging piano sonata written up to that time - and still one of the most challenging works ever written for piano nearly 200 years later.

I agree with Malcolm D: The 23rd Sonata is undoubtedly his best.

However, I love Sonata 8, 14, and 21 as well

Moonlight Sonata & Fur Elise - because lots of people recognize it and can recall certain sections of the pieces.

I'm a huge fan of Beethoven, but I find that his masculine intellectualism often hinders him from being as obviously 'tuneful' (and tender) as Mozart, for example, or Schubert. He had his moments, though, and one of my favourites is the Allegro (third movement) from his piano sonata No.4 in E flat major (op.7). It's so tranparently textured in parts that I often find it difficult to believe that it was old Ludwig that wrote it. I'm not saying that it's the greatest piano piece ever, but it never fails to calm my spirits, and that's one of music's most important properties. Strangely, no one ever seems to have heard of it...

Appassionata is Beethoven's monument to the piano repertoire.

Pathetique sonata adagio cantabile movt