Most of these services may be quite unpredictable and while they are all quite reliable including Chronic and Swift as my top destinations I also try to use others who may be less overloaded with orders. I have recently been unlocking iPhone 6 At&t through AttUnlocker.us. But I use several always and try not to put all orders with the same service. Always juggling orders between a few services sine I buy and resell used iPhone off eBay so can't risk ordering all my unlocks from one service.
I vouch for ATTUnlocker.us, they unlocked mine when the AT&T Unlock Portal wouldn't after like 70 attempts. It took them 2.5 days for them to execute the unlock.