I was a Shimano user with 9s but moved to SRAM on 10s, so some of this may speak towards 9 vs 10 speed. I now have mostly Rival with some Force on 3 bikes. Overall, my Shimano stuff seemed more reliable. I never had a 'failure', just replacements of wear items at what were respectable service lengths. I still have a DA7700 bike running and shifted one of my 105 level mixed groups on to my wife's bike and they are running well.

With SRAM I have had a couple of failures and some definite pre-mature wear outs.

Specifically, I have had 2 FDs go bad. Looking from the top, the cages would get bowed out. I could bend them back, it would happen again quicker. I have since replaced them with Shimano FDs which work fine with Sram. No failures and the set up and shifting is easier and better.

I have had one set of Rival jockey wheels that needed an early replacement due to cogs kinda wearing off the bearings.

I have also had their BBs go bad after just a couple thousand miles, even one of the newer 'improved' models. They did see some rain/winter miles, but nothing excessive and not more than my Shimano bikes have seen. But I do have one bike with an original Rival BB that has been running fine since 2008, so it appears to be a hit or miss thing.

And last, their chains tend to get ratty quicker than any others. This has mostly been the 1050/1051 model. I still use them sometimes as they are often the cheapest 10sp chain out there, but I just replace them after 2500 miles and before they go south. Since I often find them on eBay for less than $20 miles per $ is stiill equal or less than other brands, but I also use other chains when available at good prices (usually KMC).

So why do I stick with SRAM even though I do like the durability and 'quietness' of Shimano better? First, I do like the shape and double tap action of their shifters. I also prefer the simpler look the Rival group to the fancier Sram stuff and anything Shimano has out. And where some of the problems that have occurred I have swapped in a different makers part and solved it.

As for the durability, if I had one bike and relied on shop labor I would find it unacceptable. But I have a few bikes and do my own wrenching so it's never an issue to be out of a bike when some goes down and time wise it may seem like the above is a long list but it breaks down to 1 or maybe 2 extra 15 minute repairs a year. I have never been stranded do to a SRAM problem, and I keep a couple of extra chains and a BB on hand just in case. And cost wise I always seem to find better deals on SRAM stuff so I don't see that as an issue either.