Well, I can give you some specifics about the Canon model numbers you quote.
The FS series is standard definition. The "HF" series is high definition (up to 1080p). However, I have heard that the HF "R" series does not actually resolve the full 1920x1080p -- that the sensor is actually lower resolution than this and simply upscales the video. This does make it cheaper though. The HF "S" series has larger optics and costs more as a result. The plain "HF" series is in the middle. I personally own an HF100.
A lot of Canon models differ only by the fact that some have some built-in flash memory (whether 8, 16, 32, 64 gigs), and others don't. For example, the FS20 and the FS200 are the same, but the FS20 just adds 8 gigs of memory. All of them record to SDHC cards. It can be convenient to buy a camera with built-in flash memory, but it can also bring with it some inconveniences (having to tell the camera which memory you want to record on, or remembering which one contains a clip you're looking for). It's usually cheaper not to buy a camera with memory and use the money toward buying SD cards instead.
The best thing to do is Google everything. If you're interested in the FS200, for example, Google it and look for reviews and forums.
www.avsforum.com is also a great resource. Look for "owner threads" where people who own the camera discuss them and answer questions. Particularly, if there are any limitations or issues, you'll quickly see them get discussed.