Which to use?

Blu-ray, DVD, USB Flash drives, SD cards, and Web Videos each have their advantages, often a combination of two or more of these is the best fit. With broadband becoming much more common, Youtube or your existing website can be a good way to have your video available to prospects around the world without the expense or delay of postage.

Web Video

Once it is online, it's viewable by anyone in the world for free instantly if you choose.  The only limitations are dependent on the viewers internet connection.  It's possible to have high quality these days with almost no delay.

DVD-R

DVD-R is the most universal disc format offering full screen standard definition video for computers as well as home entertainment centers.  Most computers today have DVD drives, so it is convenient for clients to view right in their office.

Blu-ray (BD-R)

The newest disc format, it will be some time before it achieves the market penetration that DVD has, if it ever does.  Despite the fact there are fewer players, if you need smooth, clear High Definition video, or 25 GB - 50 GB of data on a single disc, it's a great choice.  It is possible on short projects to duplicate this format to a DVD-R as well, saving duplication money while keeping the quality of the format.

USB Flash Drives, SD Card, ect...

As far as physical media, there are many newer options besides discs.  USB flash drives can be printed with your company logo and given away with a video on it.