DVD-R was the most compatible a month or two ago. Media is plentiful and cheap.

DVD+R should be more compatible than DVD-R but media isn't plentiful yet, so it isn't as cheap (if you can find it at all).

Pioneer is the brand burner to get for DVD-R and HP for DVD+R. Both burners are between $300 and $400. I only know this because I am interested in writable DVD as well. I don't own either format yet. I am leaning toward DVD+R, but won't make a move until more media comes out.