Kinda depends what you're used to and what you get the best results from normally. I personally prefer reading books to staring at a PC screen but that may just be age/what I'm used to. I've seen some CD-ROMs that have been quite good (sorry, can't remember the name of them) when I was doing my PPL some years ago but overall, I get more out of a good book. I'm told the OAT ones are good but I've not used them myself.