I heard different opinions. But there are much more complaints about difficulties of Cup. For me, in combining 30+ seasons, I only won Cup for one or two at very low levels.
In terms of no. of participants, a CL is competed by 32 teams while a Cup is competed by 128 teams.
Now I don't concern too much about Cup, because the prize is too low. I cannot see much benefit from it without winning it all.