Bottomless Vault (along with its storage counter brethren) is strictly better than the mana batteries from Legends. They build their counters for free, and as lands they are less vulnerable to disruption. These lands don't speed your mana production per se, but they can manage to sit on the table and look innocent until (at least in Bottomless Vault's case) your opponent is on the receiving end of a massive Drain Life.

  -- By RKolbasowski from Jersey City, baby! on June 23, 2005