Should I go with "Single" vs "Vacation" for a second home I purchased and which I rent out a portion of the property?

Yes, it is considered a personal residence converted to a rental. 

The only difference it makes (versus buying rental property), is how the gain or loss is calculated when you sell it. 

Since the house was a personal residence and converted to a rental, you use the smaller value as the basis (the cost value that is used for depreciation) either what you paid for it, or the Fair Market Value on the date it was converted. 

Use the smaller amount and allocate the portion of value for the rented portion. 

Say you purchased it for 200,000

When you "placed it into service" in 2024 it was worth 230,000.

You use the lesser of 200,000

You rent half, so the "basis" of the rental is 100,000.

Keep track of the depreciation that the rental takes year after year. (You have no choice, you can't "not take depreciation".

When it comes time to sell, you will need to address the depreciation recapture.