Sorry - it's sort of an "it depends" thing.:)
If you are approaching the climb after barrelling down a nice big hill you might be in 3-8. If you are approaching the hill from a long flat you might be varooming along at a nice pace on 2-5. If you are approaching a pinch at the end of a more gradual climb you might be in 1-4. And yet again - what suits me to approach these might not suit you.
Practice will tell you what you need (just keep trying different things until you find what suits you) and then over a period it will become quite instinctive to select the right combinations for your legs when you see that hill coming.:)

