My car's color is #305 (metallic blue) - Am I better off getting a paint company to match the color (with chips) or can I get original colored paint from an aftermarket company/dealer?

Any Automotive paint company can match DN305 sky blue metalic!

Any recommendations on a company?

Get a good well known(and proven paint system) in a good brand(most manufacturers have several quality levels of paint) Martin Senior and Sherwin William are two I have used with very good results

Wait!...if you are after chip repair, visit a company with computerized color matching-light blue metallic fades fast(comparatively speaking) and if you try to match for chip repair with a factory color mix, the odds are the repairs will stand out because the new paint is darker-even if only several months old(here in South Georgia).

If you are painting the whole car, get a factory match to DN305, if you are fixing chips take the car in and have the color computer matched(using your existing paint) to the the most noticeable chips-or have it averaged and mixed.

Will

If you are looking to repaint the entire car, talk to your painter about what you expect, in detail. In my case, my car's 905 red had faded to the point that many people called it orange. After discussing it with my painter, he selected the closest pre-mixed color to 905 from his preferred paint manufacturer, then custom tinted that to match the underside of the toolbox lids. Turned out great!

Different manufacturers make the same colors different. Omni sucks for matching but PPG has been spot on in my experience. If you want to paint a hood or fender etc. you may want to take your car to your local auto paint supply dealer. They can use a UV light gun that will read your current paint. I did this with my 510. I believe this will account for fading. Ask the specialists to make sure though.