I hate to break this to you guys but honestly, the top of the line engines from all the top manufacturers are pretty even, you would be hardpressed to really see a difference between two engines that are properly tuned.
I hear people raving about the C5 BB or C6BB yet Rody Roem, the guy that designs the RB engines admits that the WS S7 series is just as strong as the C5/6 series.
they just deliver power in a different way, suitable to different conditions.
Now reliability is an area where you can really make bold statements because some brands are just plain more reliable and durable than others.
in my experience, the RB's seem to have the best build quality but that's another subject .