The prose version is, simply put, much better. The story flows better, the character motivation, personality depth, interaction & development are smoother. The events can be a bit haphazard in the graphic novel, especially vol 1. The prose version is also, of course much more detailed regarding both the characters & world-building (there's a lot of interesting things about Taldain you'll miss if you only read the GNs!). Things gets better in vol 2, and I actually like vol 3 better than its corresponding part within the prose. But that's still only 1/3. I'd recommend reading the prose version and getting vol 3 of the graphic novel (the ending is better, and there's quite an interesting additional scene).