I have the current vintage of 105 on my bike, and it works well. The rear shifting is very smooth and crisp, both up and down. I would say it is a bit less crisp in shifting from the small to the large chain ring, but this is also going up 16 teeth (I have a compact double). I also like the fact that you can trim the front derailleur
I don't have much experience with Rival, other than a couple of test rides. But certainly Rival has attracted a lot of fans in a short time, and it is noticeably lighter than 105, especially the brifters and brakes. (weight-wise, Rival is actually pretty close to Ultegra).
A new version of 105 is supposed to come out this summer. My guess is that it will up the ante a fair amount - one thing that I think is fairly certain is that the derailleur cables will no longer come out of "the sides" of the brifters, but will be hidden (as is the case with SRAM and Campy, and is also the case with the latest Dura-Ace and Ultegra). Probably the weight will drop a bit as well.
I don't think the new cable routing is a performance advantage - but it looks a little neater.