Have tried both and prefer the first option myself as both a developer and a user. From the development side, it's more straightforward and easier to implement. It doesn't have to be boring, either - you can still create an aesthetically pleasing layout (be sure to specify a print stylesheet and test it). As a user, the information is more accessible than when it's in a PDF, it loads incomparably faster, and if I
want a PDF, I'll make one myself.
But I've gone the PDF route for clients who want more meticulous control over the appearance of the output. For that I've used
FPDF to create the file and served it as an attachment; this works fine cross-browser. Development takes longer as it can be hard to predict how the output will render, so I found myself editing and re-checking a lot.