OSRS | Colosseum Sol Heredit kill (80+ attempts) 

easier.. its 12 waves not 69.. so way faster to get more attempts/learning in than having to screw with 50+ waves to get to the hard ones and zuk again

@@suffer8318 mechanically sol much more difficult, but as you said, endurance is the challenge of inferno.

I would say overall Colosseum is easier than Inferno. Although, waves in the colosseum get hard quick, and are more complicated than Inferno. Inferno waves are slower and easier to solve. BUT Sol is more forgiving than Zuk, there are no one-shots. With Zuk you have no room for error. I would definitely do Colosseum instead of Inferno if I had to choose.