I'd get the 2 way (-r and +r). Although I have -r my sense is that +r will eventually capture the market. Not because it's so superior in itself, but because of several advantages -- faster burning (more than twice as fast for RWs) and just the fact that a huge retailer like Best Buy no longer carries -r, only +r. This tells me their marketing department has made a decision that +r (in their opinion) will win out and is the better format. Whether they're right or wrong they have huge influence over public buying habits by their choice of what to carry and what not to carry. Also, whatever you get, make sure you see the posts here about the proper disk media to use. If you use -r and don't get the proper media you'll be making coasters (example, for -r you can forget Memorex, although their +R media may be OK).
I'd get the Sony if it does both -R and +R. I have the HP200i (+R) and the Pioneer A04 (-R). Having the ability to write to both types of media has expanded my compatibility with my clients. I had given a -R DVD to a client that couldn't play the disk. As it turned out, the model DVD player they had was listed as not compatible with -R, and I didn't not know that at the time I gave them the disk. Then I gave them a +R and it worked great.
Just bought the sony dru-550a. Had a problem with sound dropping out on one clip out of 4. I lost quality in the rendering to dvd format from vv3 dv format. used -r, and I'm seriously considering taking this back. DVD format is to expensive for this lack of quality and reliability.
The question is whether set-top boxes will stop supporting DVD-R. Personally, I doubt they will, and with that in mind, I'd go for the A05 when it comes out. I just got the A04 a month ago and love it, and I mean sexually. I may get an A05 when it comes out just for the speed, but don't tell my wife. Of course, it's the rendering time that is the real killer. 0.5 hour to burn a DVD doesn't seem that bad compared to how long it takes to render a file to MPEG2.
I think the -R or +R issue is going to quickly fade away, simply because the new DVD players will play either just as well. Given that, I think -R will have the volume advantage for a long time. Furthermore, I have read that the -R gang has about a 6-month head start on faster drives. For example, the -05 is coming out very shortly, while a faster +R drive is supposedly scheduled for spring '03.