I think cur2 only if you're on a killing roll. Get 2 or 3 kills on them early and you've got your basic hp/mana build then maybe cur2... but remember if you bought sigils and robust pots instead then you're more likely to avoid death in the field and push the enemy off farming.
No point spending 3k on cur2 if you're going to be pushed back all the time for regen and miss out on the farm gold eh. As rook or OCulus a robust pot or two can earn itself back because you farm the shit outta those creep waves and push your enemy back denying him the same. The more of your creeps that get wasted on towers. the more behind the enemy gets.