To buy or to Trade?

which is the best solution for links? To buy them with only 1 way links or to trade them? And why?
Are blog links more powerful than normal sites?

Example:
I had a link exchange program and had about 500 links /month with any kind of website or PR...i had the link pages with nofollow and .htaccess restricted for robots
I've got PR3 for all my site pages--about 15...even for the portfolio ones

I've stopped that and bought some PR3-4 links
After 1 month google sent me to page 4 instead of page 2 for web 2.0 design keyword, and even took all my pr leaving me a PR2 for the homepage..

Strange right?

 

It is best to bay links, they are worth more on search enginec insted link ex.

 

and what about rankings?

 

One way links

I don't waste time with linkexchanges ...

 

So the guys that you exchanged links with accepted the no follow ?

 

it was a link exchange website where the links are checked automatically..you don't review them yourself...at 500 links