As I see it, Roche path feels more unique and has more Roche whom Iīve found to be my favourite character featured in a computer game released in 2011. It also features my favourite funny moment in the game (dicks scenario).
Iorveth path feels more traditional, delivers a bit more gameplay/questing variety (as well as more side quests), feels somewhat more connected to the first game (mainly because Dandelion and Zoltan are more involved), and the overall story feels a bit more fleshed out with it. It also features at least three LotR references which I didnīt find funny.

I prefer Iorveth route because the whole game feels more "meaty" with it, however in hindsight Iīve found Roche route more memorable, so itīs pretty close.