Hi Mhd, hard decision isn't it? I have the 1:8 and am considering the 1:4 for its low light capabilities. Both lenses are rated highly, especially for the price (the 1:8 gets down to $198 these days, the fastest lens you can get for anywhere near that money!). On this site
http://www.naturfotograf.com/lens_surv.html they are both rated 5 out of 5. I have also read that the 1:4 is sharper between 1:4 (it would have to be, the 1:8 doesn't go there) to 2:8, they are the same to f4, then the 1:8 is sharper. I cant remember where I read that, and may I state I don't know, just repeating what I read. Don't pay too much attention to Maxwells website, if they were absolutely correct some of the lenses would have as a description "this lens is created to stop consumers buying cheap ordinary performing third party lenses and instead buy cheap ordinary performing Nikkor lenses"
Good luck
ps Gary and Birddog are two who have the 1:4