Welcome and congrats. Both are great bikes, I tend to advise new riders to start with a smaller bike. I would suggest the 550, it's about 100 pounds lighter, easier to maneuver around when parking, etc.
The stock seat height on the 750 is a little higher too, that may come into play depending on your height. Shop for go look at both and try them on for size, you may answer your own question.
BTW - where are you?