SRAM Red? Shimano Di2? Campagnolo Super Record? What's the difference?

I've got some good info brewing, just trying to finish it up:  aesthetics aside, where do you get the mostr bang for your buck?

A little teaser:  Did you know that SRAM Rival (3rd tier) costs less than Shimano 105 (also 3rd tier) but weighs less than Shimano Ultegra (2nd tier)?

More later

J