Computer. The only time I ever had an issue was when an FFL mis-read my writing on the 4473 while calling it in. Luckily, I heard him make the mistake and told him as such when he came back with a delay. He called right back and it was corrected and a non-issue.
My LGS uses a computer. I like it, mine always take at least a minute or two, but nothing to complain about. The few times I've been delayed it's been maybe an hour or two. Wouldn't matter as far as that goes if it were computer or phone so I can't complain.
A buddy of mine always takes 20-30 minutes, whether it be phone or computer. He was told it was because of a Top Secret clearance from his Military days.
My LGS phones in. Takes just minutes. Made a purchase at Cabelas (on sale and only place I could find it....) and the computer took FOREVER!! Granted it was mid-December so might have been a Christmas rush.
Here locally they have always used the phone, but was out in terrehaute and my brother found one he couldn't live without and they used the computer, like most have said we haven't waited longer than 10 min from start to finish