I have the Timbuk2 Especial Viaje convertible backpack/pannier which I use to commute with my work laptop, a MBP 15" Retina. It uses the same rack-attachment hardware as the current edition of the Timbuk2 Shift. That hardware has broken 4 times in my ~8 months of owning the bag. Timbuk2 has been good about sending replacement hardware, but it's still not fun to have to maintain the bag that much, especially considering Timbuk2 sells their bags as being very durable. They're now offering me store credit to get a new bag, but they don't have any equivalent bag currently available, and won't until 2015, so I'll take them up in fall after the hot, sweaty summer is over.
I wonder if they only tested the all-plastic hardware in SF's very mild climate, as opposed to somewhere with seasons— perhaps using the bag through the winter weakened the plastic?
I also had a previous edition of the Timbuk2 Shift, which had even worse pannier hardware with 2 hooks held in by tiny little pins as its only points of support. When one of the hooks fell off because its tiny pin slipped out, I was very lucky the bungee the bag had didn't get caught in my rear wheel and cause a crash, which would have been especially bad in lower Manhattan traffic.
So, I guess my answer is: I suggest the Ortlieb as they're a lot more experienced with manufacturing/sourcing durable pannier hardware. Or maybe look into the Arkel as well: http://www.arkel-od.com/us/messenger-pannier-laptop-bag.html
If you do want the Shift, REI has it:
And it's nice to be able to take advantage of their return policy, if you need it as I did.