They both work extremely well. Buy the cheaper one. Buying the Pioneer does not give you much of an advantage that I know of. They either burn DVDs or they don't, right?
Over time I have had several Pioneers and quite a few LGs. You won't catch me springing a woody over the Pioneer, because for what I was doing I didn't notice anything spectacular about it. It's just your typical burner as far as I could tell.
I will tell you this. I have a Pioneer DVD player in my rig to this day. I have had it for probably 7 years. It is screwing up a little bit, quickly opening and then closing again when you press the button, but other than that it works fine. The other one that was it's mate and bought at the same time died on me about a year ago. Maybe less. I would say that's pretty damn good service, wouldn't you?
Now I have 2 LG DVD, 2 LG DVD/RWs and several other assorted brands in the servers. The LGs have been great to me so far. No coasters, no glitches, nothing. I'm really happy with them.