What do you mean? 13th Warrior was a cool movie but it is in no way similar to Beowulf other than they both depict Nordic tales. If you're just comparing the two epics...I'd have to go with Beowulf, I mean, it's a total gem of literature. You're not going to find Welsh literature from the dark ages (or any sort of European literature from the dark ages) in many other places. It gives you a pretty good look at what was important to the people of the day.
the thirteenth warrior is the entire life of beowulf combined into one battle for the movie- in the view of the poet who originally wrote the down the legend; the main character in the movie, the arab
Beowulf is one of my favorite works of literature, so i naturally find it difficult to compare to the 13th Warrior. however, to the movie's credit, it does not seek to be an adaptation of the old English poem, but rather a retelling with a different perspective and some different twists. interestingly, there is a well-known account by an Arab historian of a meeting with the Vikings in Russia (i think that's where it was), so i wonder if that was the inspiration for having the story told through the eyes of an Arab. by the way, i highly suggest J.R.R. Tolkien's essay "The Monsters and the Critics" as an excellent commentary on Beowulf. it gives some interesting and likely accurate perspectives on the purpose and nature of the poem that most readers would not think of.