For those who have been to either or, which one would you prefer? I'm a 21 year old girl, and am doing a trip around Europe (mostly Europe) for the summer with a friend. I will be staying for 3 days. If this didn't work out I was thinking of Florence as well.

Any tips would be helpful!

Istanbul has more to offer, it is more European, and the people are not as aggressive in terms of asking for money as in Morocco. Example: You ask for directions and the person leads you a couple hundred yards in the right direction. He (and it is inevitably a man) will then ask for payment and quite aggressively. I was swarmed by kids trying to pick my pocket. I liked Morocco, but my wife found this constant hustling too much.

Interesting, I find Marrakech sort of "Arab easy" that is the begging is very low key, the pressure to buy very low and people very friendly. The city is a delight with a great new airport, wonderful old town and pleasant "European Quarter", plus of course everyone knows hastling wealthy Europeans is the best way of making sure they stop coming.

I think the real question is how hot Marrakech will be in the summer ( I see it as a winter destination).

Having been to both in the summer I would choose Istanbul. It is a great city.. so much to see and do. I found the harrassment factor to be much less in Istanbul.. but Marrakech is more exotic..

Both are absolutely wonderful, but I would choose Marrakesh in a heartbeat.

Both are wonderful places, but the water swings it for me. Istanbul is surrounded by it. You can get ferries all over the place, sit and watch the world go by around it, and eat fantastic fish. From Marrakesh you have to get out to Essaouira, to the coast, about 90 minutes away. But that is spectacular too, beautiful clear Atlantic light.
Can't remember much hassle in either, possibly in the souk in Marrakesh, certainly not in the Grand Bazaar in Istanbul.
Istanbul is easier to get around, there is an infinite amount of public transport, ferries, subway, funiculars, cheap taxis.
If you're interested in history (not everybody is Istanbul wins hands down.
Have been to both in summer and I think Istanbul is cooler simply because there is all that water around. In Marrakesh you get the hot desert wind.

Istanbul, no question - more history, better food. If I were going back to Morocco, I'd pick Fes over Marrakech - much more interesting and less touristy medina.

I think I'd pick Istanbul for the variety and the history, but really either one is pretty exciting! Marrakesh is unique and exciting (and not nearly as in-your-face as Tangiers, which I really didn't care for much at all...probably due to having been in Fes and Marrakesh on a previous trip.)

I agree with thursdaysd, Fes anyday over Marrakesh, which I found to be rather over-rated and touristy, Fes was a quaint little gem. That said, Istanbul might make better sense, especially since you'll be traveling in summer.

After coming back from Istanbul, I'd say Turkey. Great public transport, beautiful city and interesting finds.