DVD+R with bitsetting to DVD-ROM (which 1620 supports out of the box) gives the highest compatibility. I've seen a friend player that only takes -R and it can read +R with dvd-rom setting. However I've also read some (mostly ancient players) cannot read +R with -rom. It's your choice but I would go with +R bitset to DVD-ROM.
Bestbuy is currently selling fuji 8x DVD+R (media id YUDEN000T02) for 8.99 25pack. Make sure you get the Made in Japan. It's a good media. Verbatim 16x DVD+R is better in my opinion, but no sale currently, a buck a piece.