I've done both and have settled in with the rolling carry-on. But I have to admit I just put all my stuff in the carry-on bag. If I had a big suitcase, I would not bring a second piece of luggage. You're not traveling the world to haul crap all over it are you. Why do you think they call baggage baggage? 'Cause it's the stuff that's weighing you down. If you have a real suitcase then just use a small day pack as your carry-on.
You might ask your friend what he or she is doing. It is nice to be doing the same so that you are able to move around by the same means. If you think you will walk long distances, the backpack may be better. If you will pop your stuff into a cab and stay in nice accommodations the wheelie is the better choice. Backpack might be considered tacky in a 4 star hotel.
Pack light!