That's a hard question to answer adriand,
I believe your best bet is to try a few various brands first, remembering that the player itself must be capable of playing back DVD-R (although over 90% of players can...)
http://www.vcdhelp.com/dvdplayers.php is a good source of compatibility.
To give you at least a basic answer, I've yet to hear of any problems using standard DVD-R (ie £5 / $5 disc made by Panasonic or TDK etc), nor have I heard of any problems with the much cheaper Vivastar unbranded (both of which play on my various players).
Princo have had good and bad reviews, so try before you buy loads...
Hope this helps,
Ian