I use the FT232BM chip, while the transport is the USB link, all software see the device as a hardware COM port. So if you have 2 com ports, it becomes COM 3 and you write your code to talk to COM 3. Think of it as a "virtual" COM port, their driver handles all of the USB bridge protocols to RS232. I've used it in several projects and have had zero issues. And it is fairly cheap. Also remember, that the maximum speed is determined by the two devices connected and whatever a true hardware com port would be which is what 230K or something like that.

The driver also has options that can be set for timing and RTS/CTS options.......pretty trick little chip.