To Terracotta Army, which transportation option is better? Wild Goose Pagoda or Xian train station?

You are advised to take tourist bus line 5 (306) from the Main Railway Station to the attraction because it has less stops than 307. I think it's more convenient.
By the way, you may take bus line 500 from Big Wild Goose Pagoda to the Main Railway Station. Or, you can take a taxi to there directly. The cab fare is about CNY 20 in the day time.