If you're in the Salt Lake area, the buses are rarely so crowded that bringing your folding bike on board is an issue. I take the bus to work every day here in SLC, and I just started riding again now that it finally stopped snowing (though the threat of snow tonight is making me rethink that decision).

While I agree with others that a used Brompton would be best for bus and shopping, it's not so easy to get a used Brommie in Utah. The bike I use for multi-modal commuting (bus, Trax and bike) is my Bike Friday Tikit. It's not as perfect for your needs as a Brommie, but it handles most of your needs well.

As for the bikes you listed, the smaller the bike, the better... so my recommendation would be the Dahon Curve. The other two bikes will work, but the Curve will be the friendliest for the bus on those rare occasions when the bus in SLC is crowded.