Hi Juls,
It really depends what you intend to do with it. A CDC device is typically used for modems, and would be the obvious interface if you're building a modem or similar device. If you need USB simply to re-flash firmware, it might not be appropriate.
I have hooked the FTDI FT232RL chip to the SCI, and I doubt anything else is easier to implement. But there are sacrifices with that approach.
With the FTDI approach, you can configure the FTDI chip to act as a virtual comm-port, or configure it as a custom device. You have no firmware to write if you already have SCI firmware (as I did). With a virtual comm-port, you also have no host driver to write. If you need to write host software, it is simpler if it is written for a comm-port.
But the final interface would not be as flexible as with a native USB device on a JM processor. It also would not be as fast, as the fastest SCIs are limited to 1 mega-baud. But then again, there is the USB firmware to write and maintain, which is far from trivial.
In my case, none of the JM devices had the peripherals my application needed, so FTDI was the obvious answer.
Just a few of the things to consider.
