I think the fish don't really give a damn, and can't really tell the difference!
fake is cheaper and you don't have to worry about it dieing, BTW- There are some really good looking fake plants, they cost like 6-8 dollars each, but I can't even tell the difference if it were shown to me without the label saying plastic!
Also, if you don't have the right conditions for some live plants, you can always get them fake!
Although If I had 1 million dollars, I would get real plants, but if you don't wanna hassle, spend lots of money, and go around millions of LFS's to find the plants you want, fake plants aren't really a big step down at all.
BTW- How would the fish prefer the live ones? How would they even tell the difference? Granted some plants are sharp, the good ones are not, so they will not hurt the fish at all, C'mon, you can't really expect a fish to tell the difference between fake and real plants.