QR codes are perfect in certain places for quickly interpreting a complex url. A presentation is not one of those places. Although a QR code is simply read by any appropriately equipped smart phone the actual mechanics of using during a presentation mean that it is usually ineffectual and often adds to confusion. There are better ways of transferring a url to the audience.
Most smart phones are able to read a QR code but this requires a specific app on the device. In some instances this has to be downloaded in advance. Not all those who have such an app are actually aware of its existence, location on their device or even how to use such technology and this poor strike rate will limit the value of such a link to the audience as a whole. Moreover for even this to be effective it requires the whole audience to stop, find their phone which may be deep within a bag, find the app, open it and then activate it. This will both take time and is likely, due to its less than universal use, lead to conversations and confusion amongst the audience. None of which is ideal.
The use of a downloadable handout is a valuable way to furnish an information hungry audience with data but at a time convenient to them that does not distract from the delivery of the presentation. The problem with a url is that for it to work it has to be completely accurately recorded and this, as described above, also takes time. The use of url shortener such as google or bit.ly will drastically reduce the text involved. My favourite is tiny.url that has the option of a custom ending that is more easily transcribed and is memorable
If you’re going to use a downloadable link in a presentation, signpost it, perhaps leave it up during questions and back it up with a short link.