I have no hesitation in recommending that you go up in the Funicular. That way you go up 320 meters in 8 minutes. Even if, unlike me, you have the choice of walking up, the Funicular means that you can spend your time at the top walking some of the marked paths which look beautiful and fairly easy - or do your own thing for a longer distance. It is worth saying that there are very short lifts at the top and bottom, enabling people with prams to get in and out without trouble and making it possible for many less advantaged people to get up.
The views from the top are quite magnificent and it is worth just strolling round and enjoying them before you think of anything else. If you want an icecream or a snack to aid your enjoyment, they are available and there is also what is said to be an excelent restaurant. The town is laid out below you and beyond that are islands and channels galore.
The shop which sells postcards will laso supply you with a guide to the various walks and you could well spend quite a time doing a few. Do walk down if you can, even if you cannot think of doing any uphill walking. The views all the way and the close-up views lower down of new and older housing are wonderful. Most of the way is like a rural stroll - even though it is only minutes from the centre of Norway's second city. Moreover, unusually in my experience, the fare for up only is exactly half the fare for the return trip!