Cash sitting in a bank account.
Agreed - the Subie has a lot of depreciation left so I'm highly inclined to sell it.
Okay, in that case just pay off the whole tax debt immediately in a lump sum.
(I'm not very familiar with how tax debt works; for all I know it's possible to negotiate a discounted settlement or something. However, I'm not inclined to suggest you do that since I'm also a taxpayer!)
Selling the Subaru and replacing it with a cheaper car is the best option, but if you decide to keep it then do
not pre-pay the 1.49% loan. Instead, invest the $13K in something reasonable, like a stock index fund (in your retirement accounts if you aren't already planning to max them out this year, or in a taxable account otherwise).
(In fact, take everything left from the $40k after you've paid your debts and sorted out your car situation, and invest it.)