Well, I've owned the Line 3, and the VK30. The Line 2 doesn't have near the power supply development that the BAT VK30 has, so, for even money, I'd select the VK30.
But on average, I've not found the 30 to be priced as low as the Line 2 on the used market. If you are considering a used preamp, I'd consider the 30 the better value overall. All prices of SF gear have been kinda volatile the past 6-8 months. Not that it means anything, but I'd feel much better having my money invested into a BAT VK30...unless of course you've absolutely have to have that hockey puck!