I own both drives, and I think that the LH-20A1H is far superior. To tell you the truth, I have only used my GSA-H42L for LightScribe after I got my LH-20A1H. The LG burns the image about ~5 minutes faster with enhanced contrast ratio enabled. Otherwise, the Lite-On is superior in every other way on my rig.
My LG is riplocked at 4X with poorer error correction whereas my Lite-On can rip at 16X+. It lacks C1 and C2 error reporting. It likewise lacks booktype setting to the EEPROM and all of the other cool Lite-On features.
What firmware is on your LH-20A1H? Have you tried LL06? I thought that I'd heard of some Vista success with this drive; maybe not. Also, with the tighter restrictions on drivers and such, does anyone know if it's even possible to crossflash/upload unofficial firmwares onto the drive under Vista?
All in all, you'll probably be disappointed with the performance of this drive. Sorry. If you can't wait for Lite-On to release some form of compatibility, it'll do. The burn quality and LightScribe labeling are rather good; it just sucks at everything else by comparison.
edit: I forgot to mention that my LG does in fact get better burns on MKM003's (Verbatim 10X DVD+R DL).