I can't pick just one !!!

u can put more than one: put all ur favorites!!!

Um. I just opened to a list of House M.D. episodes (Wikipedia) And typed down some of the episodes that I actually remember without needing a memory-refresh.

Humpty Dumpty
Daddy's Boy
Forever
Who's Your Daddy
Lines In The Sand
Merry Little Christmas
One Day, One Room
Needle In A Haystack
Half-Wit
Top Secret
Fetal Position
Airborne (Holy Cra-!)
Act Your Age
Alone - There are quite a lot of scenes throughout the episode, you got to admit.
97 Seconds
Mirror, Mirror
Ugly
You Don't Want To Know - "Bring me the thong... of Lisa Cuddy."
Games
No More Mr. Nice Guy
Living The Dream (Performance review!!)
House's Head
Wilson's Heart
Dying Changes Everything
Not Cancer
Adverse Events
Birthmarks
Lucky 13
Joy (JOYJOYJOYJOYJOYJOYJOYJOYJOY)
The Itch *squee*

Wow, that's alot RL! XD

I'll just put my top 10 down here (not in order...i can't do order right now, my brain is too scrambled, lol)

Joy
The Itch
House's Head
Fetal Position
Wilson's Heart
Half-Wit
Who's Your Daddy
Ugly
Airborne
Act Your Age

I second all of those rainbow, I'd also like to add "Skin Deep"- he drops his pants for her, and shows his trust in her, and "The Jerk"- Super sexy office scene "You are one evil, cunning woman." Also from season 1:
Pilot
Paternity
Occam's Razor
Damned if You Do
Socratic Method
Control(Vogler:Are you sleeping with House?)
Babies and Bathwater
Three Stories

Now my top 15(I tried to do 10 but it proved impossible) of all time(Not in order, idk that I will ever be able to put them in order, especially not right now lol)
The Itch
Joy
Insensetive
Act Your Age
Airborn
Fetal Position
Who's Your Daddy
Humpty Dumpty
House's Head
Wilson's Heart
Living the Dream
Words and Deeds
Half-Wit
Top Secret
Babie and Bathwater

I can't pick just one I'll put eleven episodes very important to me:D, my top eleven:) (not in order)

-->>Humpty Dumpty
-->>Who's your Daddy?
-->>Insensitive
-->>Top Secret
-->>Airborne
-->>Half-Wit
-->>House's Head
-->>Wilson'Heart
-->>No more,Mr Nice Guy
-->>Joy
-->>The Itch

Pilot
Humpty Dumpty
Forever
Who's Your Daddy
Finding Judas
Merry Little Christmas
One Day, One Room
Insensitive
Top Secret
Fetal Position
Airborne
Act Your Age
Alone
Mirror, Mirror
Ugly
Living the Dream
House's Head
Wilson's Heart
Dying Changes Everything
Adverse Events
Joy
The Itch

Wow tricky question. Well sort of tricky. My favourite episode of the show as a whole is Fetal Position so I guess that counts as my favourite Huddy episode.
But I adore all the episodes in which their relationship is thrust under the spotlight. Notable mentions would be The Itch, House's Head, Finding Judas/Words and Deeds and Who's Your Daddy.
In fact the final scene they share in WYD is still my most favourite Huddy scene of all time. The way LE delievers the line "no" makes me flail moronically everytime I see it.