My 2¢, I personally like Ultegra. I don't think the difference in performance (if any) is worth the price to go with Dura Ace. The higher level components are lighter, if that is a high priority for you. I would save on the components and spend a little more on the wheels, if it were me (but it's not).

I've got Rival on one of my bikes. The shifting is a little noisier and not as positive on the SRAM and requires more pressure on the levers. But lots of people prefer SRAM, it is largely personal. I like SRAM fine, I just prefer Shimano. No trim on the small chainring on the SRAM is another small annoyance to me.

One place SRAM really shines is braking. It has a really nice light feel and the configuration of the levers makes braking from the hoods much easier on the Rival than my 2002 or 2010 Ultegra.