Rome or Istanbul for 4 Days in Early December?

If you are on a budget, Istanbul is very expensive. We are here now and are surprised at the high prices. Besides the museums being expensive, the food is too. The average cost for a meal for 2, without alcohol or coffee and dessert, is $65.
But, 4 days is probably enough time to see the sights. Rome would need more time.

If I had the choice between connecting flights or non-stop flights, I would choose non-stop. You can eat cheaply in Rome if you don't mind eating simply.

Istanbul has great art and architecture as well , neither would be a bad choice so I would choose the convenience of getting there.

Having been to both, I might have to flip a coin. However, the Vatican Museums and Sistine would be the deciding factor for me, but maybe not for you. Istanbul gives you a taste of a completely different culture.

I agree with Barbara that 3-4 days in Istanbul will give you time to cover much of that city's highlights. I'd save Rome for when you have more time. Last year I spent 11 days in Rome and still felt like I didn't have time to see it all.

I'm actually heading to Istanbul for three nights next week using Turkish Airlines' free stopover program. Barbara, I'm sorry to learn how expensive it has gotten since last time I was there.

Moss, if you fly Turkish Airlines, you should be able to do the stopover in Istanbul, and they will give you free hotel accommodations. It might not be the best location, but free is free.

However, the Vatican Museums and Sistine would be the deciding factor for me

Do you know how easy it is to get tickets to the Vatican Museums/Sistine Chapel and Colosseum at this point -- about a month in advance?

We did find Rome to be a fair amount less expensive--the hotels, the restaurants, the sites.

One can eat cheaply and well in Istanbul, just stay out of the obvious touristy restaurants and eat in local places where most of the clientele is regular Turks. It's true that tickets for entry to the major sites can be surprisingly (and seemingly unjustifiably) high. That said, a lot of the "attractions" for me are just the city itself, requiring no "ticket".

On a more practical note, I would ask myself: which city am I likely to have more opportunities to see in the years ahead? If you travel to Italy occasionally, you will probably have many chances to include a stop in Rome. If you would be less likely to pass through Turkey, maybe this is the time to stop there? A lot would depend on your age, travel patterns and likely future trips.

Been to both. I’d opt for Istanbul. Hagia Sophia is stunning. So is the Blue Mosque. Old town vs upscale neighborhoods quite the dichotomy of architecture. Had the best meal in a restaurant on the roof of the Grand Market. Found Istanbul fascinating. Traveled solo.

For a 4 day stay, I would suggest Istanbul and especially if you have never been there.
Prepare yourself for it. It is busy but there is much to see, The food is amazing and in many ways, outshines even the wonderful food of Italy. But as has been noted, without a proper local guide, it might be a bit of a challenge. It is one of the few places where I recommend one. A guide will make sure that you get around efficiently, will save you money and will help you to appreciate what it is that you are seeing.
As a rule, I always suggest that anyone going to Istanbul to also visit Antalya or Gaziantep or any of the other places of interest away from Istanbul. Turkey has so much more to offer than Istanbul. With your short time, Istanbul might be all you can do but do take the time to learn about the other places you might enjoy. A history buff or a foody will love this country. And.....if you are offered coffee, you must accept, and do not try to rush through it.