It depends on what you are looking for. The Chromiums have a plastic covered housing with a chrome back to create that thick OEM look and prevent glare into the headlight for a crisp round light output. The thinlines create that thin neo look and is just a different look for demon eyes. There is no wrong choice, it is a matter of preference. With that said, most customers opt for the Chromiums. Here are the two product pages:

Predator Chromiums for X5
http://jlevistreetwerks.com/store/pr...5626de4674fb8b

Predator ThinLine for X5
http://jlevistreetwerks.com/store/pr...5626de4674fb8b

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