Go with the BEHR!!! I went with the Nissens and it only lasted me a bit under 12 months before I had to deal with overheating. I have a post about my ordeal and I thought that my overheating was everything but my brand new radiator. My original Behr was broken at the neck when I bought it. I just happen to check my hoses and saw that the P.O. just moved the hose forward (it never overheated even though the neck was broken so I kept it).
I think I paid about $180 for the Nissens and luckily I was able to get a Brand new Behr with reinforced necks for about the same price delivered to my door and my 126 (560 SEL) has been running just fine ever since. I did keep the Nissens for extra parts since it didn't look too bad (on the outside anyway) and will probably get it rodded just in case I need it again. My original behr is still in the garage also for a just in case scenario because it still worked perfectly although the neck was broken to where the sleeve was just shorter.
I would never risk trying to do an "easy fix" with my MB's because the money you try to save will end up screwing up the car and eventually will cost a mint to repair once it goes to a point of no return as far as engine damage from overheating and all of the miracle solutions available that claim to fix everything. I'd rather just replace with top notch parts and drive with confidence. My .02