I have to much prefer **QuickOffice 3.3.51** over the dismal D2G 3.001 on my Android 2.1 HTC Hero, although both are frustrating and could easily be developed further. Numerous reasons. I tend to read online books in .pdf, .doc, or .txt format (I can't deal with epub, mobi, etc.) Initially, I thought it would be the other way around.
These programs are suites and ideally each component would be considered separately. Take the PDF component. A pdf book might be 400 pages, and now suppose that I am on page 231.
If I am reading/referring to a long .pdf via D2G, switch to another program (email, etc.), and then switch back, D2G will have completely lost the page, and have returned to page 1! You can dig to find a 'go to page X' but then you have to know which page you were on. There is no way to pull down the cursor to get to a distant page quickly. QuickOffice does not have this problem. QuickOffice also lets you enter a pagewrap mode which makes scrolling and font size changing much easier.
Both programs are pretty screwy about virtual keyboards. I think you should be able to drag it over from the left or the right rather than fiddling on the bottom with some toggles. Both programs are impossible to create outlines - in part because there is no tab key, up down left right arrows.
D2G also abandons its initial clean file interface - to pile on useless information. I want to select which local file to open. in landscape mode, I can only see two files at a time, with an entire line taken by a directory listing, and another by the toolbar which could be a lot skinnier, then an announcement about what program I'm running. QuickOff can show 5 files at a time. Etc. Etc.