When Beleg asked Thingol to let him go find Turin, Thingol let him take any sword in the realm (save his own). Beleg chooses Anglachel, although there were probably plenty of nice Elven swords to choose from. Why is that? (Yes, I know that it was fated to be so; I mean at that time, why make that choice?)
Beleg's request was for a good sword:
'I ask then for a sword of worth,' said Beleg; 'for the Orcs come now too thick and close for a bow only, and such blade as I have is no match for their armour.'
And Anglachel was a very good sword indeed:
Then Beleg chose Anglachel; and that was a sword of great worth, and it was so named because it was made of iron that fell from heaven as a blazing star; it would cleave all earth-delved iron.
There are two key points here:
- Beleg's primary motivation in choosing a sword was to have one that could pierce Orcish armour.
- Anglachel could do this.
In fact, the second passage I quote goes on to say:
One other sword only in Middle-earth was like to it.
And that other sword was not in Thingol's possession at the time. So it's quite obvious that Anglachel wasn't just a typical "nice Elven sword" but was actually the best sword available, the best tool for the job Beleg wanted to do.
(All quotes from the Silmarillion, Of Túrin Turambar)