The correct answer is "Both". Because Kiseki no Umi is one of the greatest openings ever...
Don't get me wrong. Odessa e Fortuno was great. But Sea of Dreams? SO GOOD.
This is the correct answer.
The OVA has more beautiful music overall, and better base animation (it does overrely on stills, but it has that 80s anime aesthetic that the TV series abandons for an aesthetic that's a premonition of the fugly last gasps of handdrawn animation in the '00s.
But the series tells a much more nuanced story, by virtue of having time. It's also a better conclusion to the story than the CoHK manga is (which somehow kills off Ashram in a way that is incompatible with the middling, but canonical Legend of Crystania).
The best bit of Lodoss material, imho, is the Tale of Deedlit manga. This captures the best visual elements of the OVA anime while staying true to the story from the novels, replays, and Grey Witch manga.
I'd recommend to consume in order:
1. Lodoss OVA
2. 1995 Lodoss SNES title (no official translation, unfortunately, but this fills in the backstory a bit).
3. Grey Witch manga and/or novel.
4. Demon of Flame manga (no official translation, unfortunately).
5. Chronicles of Heroic Knights anime.
6. The Lady of Pharis manga (backstory to the entire series, it's hinted at over the course of everything that I've listed before).
7. Deedlit's Tale manga (it's told out of order so it's best read once you have a larger context of the story arcs).
8. Rune Soldier Louie manga and/or anime.
9. Legend of Crystania movie and OVA.
10. Play Deedlit in Wonder Labyrinth (takes place after the end of the entire series).
Also, if you want a very different D&D campaign setting from the same author,
Record of Grancrest War is phenomenal, and has been described by some as Fire Emblem: The Anime. Interestingly, Fire Emblem has readily stolen from Lodoss - see the villain Ashnard, who is clearly a combination of Ashram and Wagnard, for example, but also just the art style and world concepts throughout - and Grancrest is very much reversing the homage by borrowing from Fire Emblem with its crest mechanics and Fire Emblem-esque story (something that Fire Emblem would then borrow back with Three Houses). But Grancrest War has a lot of non-FE tropes too that are very D&D - vampires, werewolves, other classic fantasy tropes that fit very easily with D&D but not so with FE. Grancrest has been translated in both an anime and manga form, though they tell very similar stories.