Not so easy, right? That's a question that's sure to spark a heated Gleek debate. With close to 300 performances so far in the show's three seasons, there's definitely plenty to choose from.
At a taping of the show's big diva mash-up for the 300th song, the cast and crew shared their own personal favorite numbers, ranging from 'Trouty Mouth' to Lady Gaga and every Broadway homage in between. See which numbers struck a chord with them after the jump.
Chris Colfer (Kurt): "I'd say 'Bad Romance.' That was a lot of fun. It's not everyday you get to dress up like Lady Gaga ... unless you're Kurt Hummel."
Kevin McHale (Artie), to Matthew Morrison: "What was the mash-up you did with Kristin [Chenoweth]? The 'House Is Not a Home' one?" Morrison: "Oh, 'One Less Bell to Answer.'" McHale: "Yeah, that was mine."
Darren Criss (Blaine): "I'd say any of the numbers that the girls have sung solo. They have really good voices. It's tough. All the guys suck on this show, so ... [laughs] except the Warblers. I'm quite partial to anything Amber has sung. I always cry for no apparent reason."
Matthew Morrison (Will Schuester): "Yeah, I would say 'Trouty Mouth' or 'Hate on Me Hater.' 'No Air' -- I like that one, too. That's a good one."
Lea Michele (Rachel): "I really loved 'Happy Day' with Kurt, because everyone says 'Glee' brings you joy, and I just felt that that really symbolized the show. But there's also so many songs that we record that don't make it onto the show that are really great. Like the 'Tell Him' song that me, Amber and Jenna did. And also when Amber did 'Don't Make Me Over.' I listen to that all the time."
Cory Monteith (Finn): "We've got so many songs, you kind of forget ... I remember seeing 'Rehab' in the pilot and being like, 'Wow. This is an amazing show. This is going somewhere really special.' So I think 'Rehab' is really special to me ... and 'Bust the Windows' because that was the first time I got a little misty because it was so awesome."
Amber Riley (Mercedes): "One of my favorites was the song Chris did, 'Hold Your Hand.' And 'On My Own' is one of my favorite songs ... and 'Rain on My Parade,' of course."
Naya Rivera (Santana): "I think I'd say 'Never Going Back Again.'"
Jenna Ushkowitz (Tina): "'As If We'd Never Said Goodbye' ... that's my favorite one."
Dianna Agron (Quinn): "['I Say a Little Prayer'] was amazing ... all these people made these Web videos. There were three bearded men that called themselves the Grizzly Bears or something like that. [Laughs] It's really hard to pick one ... it's really hard to pick 100 ... I had the most fun in 'Time Warp,' I think, because I got to be crazy."
Harry Shum Jr (Mike): "Queen's 'Somebody to Love' ... that was the first time that we were almost nervous to perform for paid audiences. It was an awesome song, and it meant a lot to us."
Heather Morris (Brittany): "Mine was also 'Never Going Back Again,' and I liked 'One' a lot, especially the sign language part."
Damian McGinty (Rory): "Um, it's been a tough three years. [Laughs] It really has. My personal favorite is probably 'Jessie's Girl.'"
Mark Salling (Puck): "I don't know why, but for some reason 'Defying Gravity' really struck a chord in me. I also still get such a kick watching Sandy Ryerson [Stephen Tobolowsky] sing in the pilot, whatever that song was. Oh, 'Where Is Love?' from Oliver! I love that character."
Co-creator Ryan Murphy: "I have a couple. I think for sentimental reasons my #1 is 'Don't Stop Believing,' which was at the end of the pilot and was our first big seller. And I really do always have a soft spot for the mash-ups. I love 'Pretty/Unpretty,' which Lea and Dianna did. I just love that one."
Co-creator Brad Falchuck: "When we did 'Rain on My Parade,' it was the end of the first 12, and it was this little club that we were in that we were doing it ... it was a very sort of powerful moment, and Lea obviously killed it, so I always love that number. I also have a soft spot for 'Hell to the No' [laughs] ... Ian's lyricism is something to be admired."
Executive producer Dante Di Loreto: "This Adele mash-up, followed by 'Trouty Mouth.' [Laughs]"
Co-creator Ian Brennan: "I was gonna say 'Trouty Mouth.'"
Now it's your turn: Tell us your favorite number in the comments!
Sneak peek at 'Glee' Season 3 cast photos, class picture style.