As much as I like reading manga online I hate to be chained to my laptop just to read. So I soooooo prefer physical volumes. Sometime money is not an issue besides I can always trade away volumes for other volumes I'm looking for. But a + about online reading is that you don't have to pay inflated prices on OOP volumes. Then again being in front of your laptop does strain your eyes. lol
Printed issue of course, because I can just read it anywhere and it doesn't strain eyes much compare to read on computer/laptop/tablet :] But printed copies have weakness too...they are not so durable...they can be easily lost due to misplace or friends that borrow but never return or unfortunate disaster like flood, and it consumes lots of storage space. I used to have more than couple hundreds of manga, but nowadays maybe only about half of them that are still not lost.
definitely printed volumes. However i would be much more inclined to spend money on them if they were printed on some nice high quality gloss paper. Because so much manga is printed cheaply on dullm almost brown paper. As far as quality goes i probably prefer monthly magazine releases... But i guess that's just me being pedantic