1

Hi!

It depends what would you like to see.
You can easily spend 3 days wandering around Delhi temples and monuments.
If you have extra day, you can go to Agra by train, visit Taj Mahal and Agra Fort, and be back in Delhi by evening.

I usually stay 2-3 days, primary to make sure my baggage arrives safely before I head to the mountains. :)

2

I was there last week for 4 days including a full day in Agra/Fatehpur Sikri.
I agree with #1. I recommend the Sikh and Jain temples (next to each other) , and the markets including Delhi Haat
My vote is 2.5 days if time is short and if the day saved can be used well elsewhere eg an extra day in Rajastan

3

Don't waste your time in delhi if you have a choice.One of the most polluted cities in the world.India ranks it the most dangerous...That said,you should take a day trip to Agra.And I suggest a visit to the Lotus Mosque in Delhi...Being trapped in Delhi rush hour traffic for one hour is the same as smoking a pack of cigarettes on your lungs...2.5 days is plenty.

4

Interesting
I found the traffic in Delhi much BETTER than Mumbai.
In NEW Delhi traffic is very good in parts due to wide roads and roundabouts (aah the "Britishers", as the Indians call them)

"One of the most polluted cities in the world"
The whole of the 4 days I was there (last week) , the whole city had terrible visibility due to a permanent haze, which the delightfully named Sheila Dikshit (Governor) blamed on Pakistan !!! (burning off)
During my daytrip to the Taj Mahal, the whole building was almost invisible from beyond 200 metres.

5

Delhi is the historical center of Pre-Raj India... and worth spending time in...

Old Delhi is where the Red Fort is...and is an important Mughul site that most tourist see before they leave for Agra... But Old Delhi can be a bit shocking to the new visitor...because its very very crowded...

But interestingly...the south of Delhi...further south even of "New Delhi" which the British built just before leaving India...is the "real" historic Delhi... You can get there by Metro...or Tuk Tuk or Taxi...

Here will be found the older tombs and forts of the Lodi dynasty who ruled Delhi before the Mughuls took over....

All of the pre-Mughul tombs and forts are very much in the south of Delhi...which is really the more fashionable part of Delhi... If you want to avoid serious culture shock...go to New Delhi first...and to the South of the City for an almost Western looking part of the city...with many "historic" parks...

Basically..."Really Old Delhi" is south of New Delhi...!