Try Gothenburg first my dear
Guaranteed to get you closer to Liseberg, which is in, erm, Gothenburg
Unless there's a reason you're heading to the other side of the country?
We flew into whichever one Ryanair flew us to (which was probably the moon knowing Ryanair, but if it's within 120,000 miles (give or take a light year) they'll claim it as local).
We got a bus which cost about a fiver and took around half an hour to get into the city centre. Liseberg is about a 15 minute walk from the station.
Edit - Damn, took too long to write that didn't I?