Can someone please tell me about these devices?
As some seem to be USB2 and others firewire.
Which is best?
If I use a firewire model can I also use other firewire ports at the same time i.e. capture video etc ?
I have Lacie and Iomega and have used both to capture DV, they are both USB 2 and I have no problems of dropped frames, unlike my FW caddies strangely.
LaCie also make drives with both Firewire and USB2, plus a connection for powering the drive via USB, if it is used on a 4-pin (therefore un-powered) Firewire port
The advice always used to be that USB2 wasn't good for video because it can't sustain the continuous data flow of video, while firewire can. USB 2 has changed all that, provided you take precautions.
With a firewire connection, the data is handled in packets that come at regular intervals, that's how it's designed. USB polls all the connected ports and services them in turn, so, to make it work for videdo you need to be sure that there are no other data-intensive services on the USB data bus while you're playing with video. In practice, with USB2 and modern PCs, it all works well enough.
I have both USB2 and firewire drives, and they all work just fine for video.