Another vote for the Ram X Mount.

 

After much research I just ordered the RAM-B-149Z-UN7U.

I read up on quite a few mounts and I found that I was comparing all of them to the RAM Mount X-Grip.

I think if you are only looking for a dedicated specific cell phone holder there may just be a few better holders than the X-Grip, but all things considering IMO the X-Grip is hard to beat in design versatility and price.
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Tech Gripper here, solid as a rock!

 

Received my Ram Mount X-grip today.
Install was a no brainer and I'm really impressed with the build quality.

I got the 7U size which is the medium size and fits my iPhone 6s well.
For bigger phones like the iPhone 6 plus you probably should go with the 10U but the 7U would still work,

It's cold out today so I haven't road tested it yet but it seems very secure and based on others' reviews I think I'll be pleased.

Here's some pics: