Trip to granby

That might depend on where you are coming from.

24 to 9 would tell me coming from the south or maybe east and if so then no significant pass until you get to Hoosier pass between Alma and Breckenridge. 24 while not freeway is pretty good road After that no big deal and you would save yourself the majority of Colorado Springs traffic as well as Denver traffic

70 to 40 is obviously good road but you will have to deal with Denver traffic and then Berthoud Pass on 40. The pass is not a huge deal but it is a bit of slog and for my money longer than Hoosier pass. While both are about the same height you are already at about 9900' elevation in Fairplay and Empire is at 8600' (40 and 70 intersection).

if I was coming from the south I would do 24/9

Do you want to see mountain scenery or city traffic? I-25 is east of the mountains, not in them. So, I agree that US 24 to Colorado 9 is more scenic, although South Park can get rather boring.

For some ideas on camping and not-to-miss sights along US 24 and US 40, see my blog HERE.

I did 9/24 last summer and other than 9 south of Breckinridge, a OK route. Like ^^^ some of 24 is boring and hard to pass. You’ll be going downhill in that switchback section so it will be easier.

I-70/40 is probably faster if the Denver traffic doesn’t hold you up.