Yes, K-ON! is funnier as a comedy slice-of-life anime.

Hibike! Euphonium is a drama slice-of-life.

I think that K-ON! is at the top of its genre and deviates from the standard moe stuff you see in other shows similar to it. K-ON! is described as "intimacy porn" in this Nisemonogatari essay and I absolutely agree with that idea. K-ON!'s appeal is all about developing a relationship with the characters and becoming more intimate as the series goes on up until the emotional high point of season 2 which I would argue is the best and most logical conclusion for a story like K-ON!'s.

K-ON!'s first season serves to introduce and characterize the characters while the second season is when the character dynamics are in full force.

Hibike! Euphonium, while a fantastic show, I think is less of a priority to watch. Hibike is newer and prettier to look at, but I think it really depends on what you are looking to do.

Watch K-ON! if you want to get to know a lovable group of Japanese high school girls and laugh your ass off.

Watch Hibike! Euphonium if you want to see drama within a high school club and see how factors such as family and talent affect the ways of life of high school musicians. It is also full of sensory ecstasy during the performance scenes.