Board Thread:Battle Nations Discussion/@comment-5221719-20140721215903/@comment-24453214-20140721225652

Best advice is probably to wait for the next limited-time promotional unit. Many of those are great at any level.

If the "common" units in the vault are old standbys (Veteran, Mega Tank, Elemental Trooper especially) and you don't have any in your army yet, you might take a chance in the vault. Maybe you'll get something really nice.