I have to say that it is interesting to read the different responses. I worked for a summer as an intern in a senate office in DC and was involved in writing some of those sorts of letters.
The first one is a really well put together one kinda makes you feel like they really put some effort in understanding your views. It is well worded and carefully avoids commitment but looks like he understands the issue.
The second is a bit of a mess had to read it a few times to work out exactly what he was saying. He does suggest getting intouch with the copyright office to complain. Does this mean he agrees with you or is he just passing the buck as what power does that office have in passing a law? Letter could do with a little editing.
The Third is a classic. The single transferable response letter. Great to hear from you. I love hearing from my constituents. Here is what I do. Please do not hesitate to contact me again for another almost identical letter and free booklet.

You gotta love it.
Griobhta