I have two Eye-Fi cards - an older 8gb X2 Pro and a not-quite-as-old 4gb Mobi, plus a Toshiba Flashair 16gb. Maybe I've been lucky, but all 3 have been rock solid. I like the behavior of the Eye-Fi cards better, once I got through the setup - they will push new jpg's from the camera to my phone anytime I start the app. The Flashair sends thumbnails and I then need to select them before they get transferred. I prefer to have them all pushed over to the phone while shooting so I can review them on the bigger screen. Disclaimer: I'm just a dad with a kid in high school band, and this makes it easier to show the pics to my wife. She can flip through pictures on the phone easier than she can navigate through the camera.
I was perfectly happy with my X2 Pro, but found the Mobi for $10 and got it for a backup. Then I found the Flashair on sale for $20 and couldn't resist.