Any and all of them, if you can play them well.
I would guess Les Adieux, third movement--or the Appassionata, third movement. Maybe Waldstein (also third movement). But Beethoven wasn't really in the category of trying to impress an audience--remember, he quit performing regularly in his late twenties.My two cents on this matter. My own performances are always better when I'm not worried about trying to impress people ...
Any and all of them, if you can play them well.Keyword: if.It's also worth mentioning that the Beethoven sonatas are hardly show-off material; aside from it being opposite to the composer's intent, showing off often doesn't fit the music. You might get someone say "Wow, he's amazing!", but it's not a show-off-piece in the same vein as a Liszt etude.