From the Pioneer 206 on, burning quality has been considered to have gotten marginally worse.
For the LG drives, burning quality was considered to be excellent on older drives, and merely “very good” on newer drives.
But writing quality’s still considered very good for both brands’ latest drives, and steps all over the quality of the last LiteOn BD drives (and the drives don’t seem to suffer from firmware quirks, unlike Samsung’s last few drives).
Some folks have been very concerned about the lifetime of their LG 14x and 16x drives, but while large online retailers will definitely have reviews regarding the premature death of their drives, I would still say it’s a moderate negative over older drives. So build quality probably has taken a turn for the worse, but not so much that 50% of the drives will immediately fail.
Similar could probably be said for Pioneer drives. It helps that some of Pioneer’s drives (ones meant for the Japanese market) are marketed as premium options while sharing the same base design with the rest of the lineup, so the base drive design is probably good enough to keep build quality from being a concern.
So while there’s no guarantee that a drive won’t break, there’s almost no reason to recommend going for an older BDRE drive model over a new one when it comes to LG and Pioneer.
In the grand scheme of things, LiteOn’s most popular BDRE line (with 12x BD-R burning capability) also seems to have had a decent lifespan, though the sheer number of them in existence seems to lend its hand to us knowing about a problem where some drives’ lasers wear out quickly if used as a primary workhorse. But the jump from 4x to 12x (LiteOn’s prior drive was a 4x model) combined with an attempt to reduce cost and produce units for upwards of 6 different brands probably results in some questionable hardware being put out there. (Other brands transitioned through more speeds, such as 6x, 8x, and/or 10x before hitting 12x models, 14x models, 15x models, and 16x models, so R&D was probably a bit more difficult for LiteOn with its last model.)
I have no idea what Samsung’s problem is with firmware. Unless trying to work with reduced RAM and storage to hold the firmware directly contributed to them having bugs because they had to do full rewrites to handle the smaller confines, there’s no real explanation for some of the bugs. And some of the bugs persist to this day. The hardware otherwise seems fine, but they’ve focused on slim drives in the last few years.