They're both good names.
I once knew a Bronwyn (that spelling), and despite it being such a unique name in our neck of the woods it wasn't odd to say in real life. Lara might me a bit "easier" for a day-to-day basis, though I don't know how many
Tomb Raider comments she might get.
I'd say Bronwen Lara would be a good combo, but you have the middle decided already.
***
Please rate my personal name lists:
www.behindthename.com/pnl/69381www.behindthename.com/pnl/69381/117507www.behindthename.com/pnl/69381/109399hwww.behindthename.com/pnl/69381/132018http://greens-end.myminicity.com/