The difference lies in manufacturing standards. -R was first out of the starting gate and overall is slightly more "universally" compatible. This is particularly true of older units. Nowadays, almost any burner will handle both +R and -R and with bitsetting of +R media, the compatibility issue with players is just about moot. As far as formats, click on this link and it will give you basic info. If you'd like more, there is a ton of info here on cd freaks, just do a search.
Your burner is a panasonic. A useful site for now and future use is Video Help.com. For your specific drive click on this link and scroll down. As you see, +R is not supported by matshita UJ-810 (panasonic UJ-810).
Pick up some quality -R media and you should be ok...Taiyo Yuden would be a good choice...easily accessible online.