Chris - here's my $0.02, since you asked. Generally speaking, PDF will produce much nicer looking documents, but you have to do a lot of coding to get them that way (since you're generating them on the fly)... and I also don't know how fast they'll be, if you have a lot of data. (The latter is easy enough to test, however; just write a small program to generate a dummy PDF report as large as you think it'll ever get and see how long it takes.)
If you need page breaks, etc., PDF is probably the way to go.
On the other hand, if you're looking for a quick solution, text/HTML displays is probably the easiest. The biggest disadvantage (besides the obvious lack of formatting, fonts, etc.) is that you can't guarantee how the printed output will appear-- I dunno who your target user is but the general public has a LOT of different weird printer setups and so forth, so you'd probably want to err on the side of extreme simplicity (i.e. don't pack too much into a page, etc.).
Some food for thought,
Eric
