My top ten in no particular order would have to be..
1) Peep Show
2) Game On (The first series though, I preferred Ben Chaplin as opposed to Neil Stuke)
3) The Worst Week Of My Life
4) Saxondale
5) The Inbetweeners
6) The Royle Family (I absolutely adore Anthony's Character as well as Jim's)
7) The Thick of It
8) The Smoking Room
9) The IT Crowd
10) The Office
Other honourable mentions:
Grandma's House
Friday Night Dinner
Green Wing
Not Going Out
Coupling
Would agree with Peep Show at No.1 and Game On, quality!
No real order.
Fawlty Towers.
Blackadder.
Steptoe And Son.
Peep Show.
Only Fools And Horses.
Rising Damp.
Hancock's Half Hour.
I'm Alan Partridge.
Porridge.
Father Ted.
In no particular order:
Steptoe & Son
Till Death Do Us Part/In Sickness And In Health
OFAH
Love Thy Neighbour
Fawlty Towers
Keeping Up Appearances
Rising Damp
The Inbetweeners
Some Mothers Do 'Ave 'Em
Open All Hours
Peep Show
The Thick of It
The Office
Fawlty Towers
Blackadder (Series 2-4)
Extras
Lead Balloon
Bottom (2nd series mostly)
Red Dwarf (dated quite badly though)
Porridge
Comedy is one of the few things that I think has actually progressed over the years.
In these post-Office days, I find most older comedy too safe and obvious. FT, Blackadder, RD and Porridge (plus Steptoe and son) still shine through though.
Can't believe Miranda and Not Going Out aren't in these! 
Do list your top 10 and include them, Lucy! 
Quote: SimonWing @ July 9 2012, 2:44 PM BSTBlackadder (Series 2-4)
The Black Adder surely ?
Mine are.
Blackadder.
Only Fools And Horses.
Dad's Army.
Fawlty Towers.
I'm Alan Partridge.
Phoenix Nights.
Brass.
Early Doors
Keeping Up Appearances.
My old Army Game favourites Bootsie and Snudge... have got to be in there.
1: 'Allo 'Allo!
2: Red Dwarf
3: Blackadder
4: Fawlty Towers
5: Are You Being Served?
6: Not Going Out
7: Yes Prime/Minister
8: You Rang, M'Lord?
9: Mrs. Brown's Boys
10: Come back, Mrs. Noah
1. Benidorm
2. The Inbetweeners
3. Mrs. Brown's Boys
4. Only Fools And Horses
5. One Foot In The Grave
6. Absolutely Fabulous
7. Men Behaving Badly
8. Gavin & Stacey
9. Two Pints
10. The Royle Family
1) Peter Kay's Phoenix Nights
2) Father Ted
3) Gavin & Stacey
4) Fawlty Towers
5) The Vicar Of Dibley
6) The Inbetweeners
7) The Office
8) Outnumbered
9) Red Dwarf
10) dinnerladies
11-15 would be, respectively,
Only Fools And Horses
Absolutely Fabulous
The Royle Family
Men Behaving Badly
Blackadder
Father Ted
Last of the Summer Wine
'Allo 'Allo
Blackadder
Mr. Bean
Black Books
Vicar of Dibley
Are You Being Served?/Are You Being Served? Again
Keeping Up Appearances
Fun At The Funeral Parlour
Forced to choose, I would say those are my top 10. Spaced, Red Dwarf, Barbara, and My Hero are high on my list as well, and depending on the day I might rank one of them above some in my top 10. 
1. I'm Alan Partridge
2. The Inbetweeners
3. Thick of It
4. Peep Show
5. Father Ted
6. Grandma's House
7. Fawlty Towers
8. Phoenix Nights
9. Rising Damp
10. The Office
1. Only Fools And Horses
2. Porridge
3. Blackadder
4. Fawlty Towers
5. I'm Alan Partridge
6. Rising Damp
7. Red Dwarf
8. One Foot in The Grave
9. Father Ted
10. The Mighty Boosh
But this list is not written in stone. It represents what I can relate to "at the moment"...although some show are in the top five (OFAH, Blackadder, Fawlty Towers) for many years and will probably stay there a few more...or forever.
There are some great shows which I am simply fed up with at the moment (The Office, Monty Python), so they don't appear in the list although I recognize their importance. Then there are some shows which I prefer to some arguably "greater shows" because I have a great sympathy for some of the actors/characters (Rising Damp or Red Dwarf for instance). Mighty Boosh is in the list because I adore the dream(or nightmare?)-like atmosphere although I find Noel Fielding and his brother pretty annoying at times.