My Experience is that D7 + commerce, is good, as long as you don't want to handle the order in the web shop, as you can with übercart.
At lease, I've not been able to get it to work, although it should be possible.
If anyone know how to achieve that funktionality, and also add track and trace numbers etc., please let me know.
übercart for D7 is good, but it lacks a module providing flexible discounts.
When I make shops I make them in D6 with übercart, due to the two problems mentioned above.
That is the only solution that has it all, that I'm aware of.
If I'm mistaken, please let me know, so I get get the shops migrated to D7 :)