Re: 2007 Shadow 600 VLX Deluxe
The 600 would be ok, however I would try to find an older one for less money than an '07.
Have you taken the MSF course? They probably have a bunch of Rebel's there for you to ride. I don't know how tall you are, how much you weigh, or how far you have to commute, but you'll probably find the 250 too small within a week.
The 750 was considered a HUGE bike years ago, but they are almost in "starter" territory now. It would probably be a fine bike to begin on. As a cruiser, the bike isn't going to get away from you power-wise. The biggest issue you'll deal with is weight. Again, there should be plenty of nice used copies out there.