Which type of certificate should I use for code-signing a Windows desktop application?
The real answer here is that you need to be able to cover the cost of the cert, only you know whether you will make enough money from your app for it. The increase in downloads between the two is unlikely to be very big.
Taking SSL.com as an example, OV certificates are offered for 2 years at $232 but EV is $598. If you think that the fairly small percentage increase in downloads will cover this then go for it. It will look more professional that way. After all, $366 to a popular app is peanuts. But if you think your app will not be popular or won't make money, don't waste your cash.