Georgios, there are many reagents out there which all work more or less well. Check how other researchers (esp. your colleagues) have transfected the cells/cell lines you are working with. Then you still might have to optimize your experiments. Depending on your needs, you maybe also want to try the "old style" protocols which come (almost) for free: Calcium chloride precipitation and complexes with polyethyleneimine (PEI).
Thanx Wolfgang, for answering. A coleague gave me a transfection reagent which works with plasmids. I was just wondering whether anyone has used Oligofectamine for the same purpose.