My opinion: basically what Madame Arachne said.
If you’re gonna be known excellent media, and you know not to try to go hog-wild with the write speed, use an LG or Samsung external. LG drives do dislike certain disc models, though, but as long as you stay with the normal Verbatim, Taiyo Yuden, or even an occasional Sony disc, you should be OK. These drives do well with both CD and DVD burns as long as you stay within a decent write speed range.
If you’re just focusing on burning some of the cheaper DVDs and don’t care about CD burning, though, a LiteOn could be a good match for you. They can usually do decent jobs with normally mediocre media, but do not expect miracles from it. CD writing quality leaves much to be desired.
All the drives tend to do a good job with reading, from what I’ve experienced.
I like both of my LGs [both external], as well as my LiteOn external [and the internals]. I do not have an external Samsung, but I liked the internal versions. No drive can do above 16x on DVD writing without buffer underruns [except some specific situations], but they are all plenty fast enough for me.