Your best bet is to get a burner already made for external use, USB is the most versatile. Liteon has a few good models as does LG. Look to newegg.com for a start. Don't fall for anything with a brand name (Sony, HP, etc.) they are just the usual makers with a huge markup. Make sure you have USB 2.
The different DVD types, - and + are not consequential unless you have a player that is older. They can have trouble with +R. RW is just reusable like CD RWs and are more expensive and less stable. I would avoid DL as they are expensive and harder to burn. If you haven't looked at software, I can recommend AnyDVD and CloneDVD from slysoft.com
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