Hiya.

I find PDF's better because I can annotate my own notes and whatnot into them. I can also print stuff (selections, certain pages, etc.) MUCH easier. From what I understand, chm requiers certain .dlls and, at least on Win7 x64, I've encountered problems where I can't open/read a chm because it's expecting some 32-bit dll that no longer is part of Win7...so I have to go on the net to find it, download it, put it in the right place, and hope that is the only one (more often then not it's two or three files I need...but I don't know that until I hit run and it says I need 123.dll...find, dl, install, run...nope, need 456.dll now...find, dl, install, run...nope, need 789.dll now...rinse, repeat.

Anyway, PDF's all the way.