I'll pile on the "backpack or convertible MLC" wagon. If you are going to be doing lots of transfers and walking through city streets I don't think you want a wheeled bag. Personally I've got an Air Boss & Sky Train from Red Oxx and a TLS Motherlode from eBags. The build quality of the Motherlode isn't anywhere near the Red Oxx bags, but I like its layout much more. Mine has lasted for several years and a couple dozen trips though, so it isn't like the Motherlode has terrible quality. It is just that nobody else has the build quality of a Red Oxx.
TL;DR, I'd get a TLS Motherlode Weekender convertible in your situation, or an Air Boss if you wanted something that'll last the rest of your life.