In theory, both should get logged in the system. In practice, though, (I've seen this question answered in a lot of AMAs by congressmen et al.), they simply don't treat email as a constituency channel.
The amount of attention your representatives tend to give your issue is directly proportional to the amount of time you can force them to spend listening. You can filter an email; you can skim a letter; you have to listen to a call all the way through. The best thing, though, is to set up an appointment, and talk to them in person.
It's pretty easy to "filter" a stack of more-or-less identical postcards, but otherwise I agree.
It's almost a truism: if you want to show that you care... spend the time to show that you care. I actually think it's really cool that you can walk right into the office of your Congressman or Senator. Obviously you won't get past the interns if you don't have an appointment, but still... pretty cool.
The amount of attention your representatives tend to give your issue is directly proportional to the amount of time you can force them to spend listening. You can filter an email; you can skim a letter; you have to listen to a call all the way through. The best thing, though, is to set up an appointment, and talk to them in person.