For your first time, Sapporo should offer you plenty of options. All transit to the rest of Hokkaido extends outwards from there anyways.

You’re probably thinking of Hakodate curry. In addition to Sapporo, Hakodate is also worth a visit IMO. The hike up the local mountain isn’t too strenuous, and the night view from the top of the ropeway is quite nice.

Normally I would recommend Otaru as well, but that’s been swamped by tourists lately.

Time permitting, I’d recommend Rishiri for the isolation, the scenery, and the seafood. Getting there and back is a bit of a trek though, unless you’ll be in Wakkanai anyways or fancy a flight from Chitose.

The best parts of Hokkaido in my opinion are the central and eastern parts, where there are a lot less people. You’d need to be able to drive though, as public transit is sparse.