It will be around for a while, though blu-ray and other stuff is coming.
In my empiric studies, dvd-r/w is more compatible, but that might not be the case in the states.
No idea about popularity, but again I'd lean towards - rather than +
-M
(+) is the new generation of DVD media. I backup my DVDs using (+) media and I haven't come across a single DVD player including PS2 that wasn't compatible with (+) media. You could spend the extra for +/- recorder, but I feel it's just a waste of money...