You can use either -R or +R, not much in it these days.
If you have an older DVD player, then this might get on better with -Rs and/or +R which has been bitset to DVD-ROM (due to some older players' compatability issues), but as I say with modern standalone players this isn't usually an issue, so go with the first ones you see/pick up.
Regarding rated speed, i.e. the speed shown on the pack, as with all speeds of disc, you get good ones you get outstanding ones, and you get your crap/mediocre ones. Once again, use the speed of disc which floats your boat, I have 4x/8x/16x in my stash.
As far as burn speed goes, I just burn at 8x 'cos with even half-decent media it's pretty much foolproof. With decent (TY/MCC) media, 12x will, in most cases do the job just as well (of course, this is dependant on burner and firmware too).
My results even with YUDEN000 T02 (TY 8x +R) with my own NS50 drive, however, do not scan at all well...no idea about playback issues. So I burn those at 4x. First drive I've come across where I've felt the need to do that. :eek:
TYG02 = 8x DVD-R made by Taiyo Yuden, TYG03 = 16x DVD-R made by the same.
As for Disc Quality Scanning (which you can do if you own a BenQ/LiteOn drive), take a look at the Stickies in the Disc Testing Methods & Software forum.