I left out films such as Indiana Jones, Die Hard, Bourne, Alien, etc. since they're no longer trilogies, also omitted Avengers because it's getting a fourth film. 

Anyways, of the choices given, I'd have to say the Lord of the Rings trilogy, all 3 movies were absolutely mind-blowing. It's also one of the few trilogies that gets better, and not worse with each installment. It pains me to say the Matrix trilogy doesn't pass the muster test (speaking strictly for myself) despite the original being my favorite movie with the shitty third film and the disappointing second movie. 

It was a tough call between LotR and the original Star Wars trilogy, I ultimately went with LotR just because of the quality of the third film in each series. While Return of the King eclipses the other 2 films, Return of the Jedi was a step back from the first 2 original Star Wars movies in terms of quality, so I voted Lord of the Rings just based on consistency.

The Evil Dead trilogy.

I love the Back to the Future and Spider-Man trilogies!

Also, the Toy Story trilogy is something worth mentioning as well. It's still technically a trilogy, since the fourth one hasn't come out yet.

Talking quality Lord of the Rings by far. Amazing movies.

I do love the original Star Wars trilogy as well though, and I’ll have more fun watching it.

Lord of the Rings, Back to the Future, Rurouni Kenshin, Ip Man (although the 4th one will release later this year or next year)

There are I guess many that people could enjoy. LOTR has the most won Oscars out of any franchise, some of the highest critical and public acclaim and my personal best movies of all time (longest extended edition there is of course so watch the 3h50m to 4h20m per movie versions and not 3h to 3h35)

I enjoyed LotR the most.

No offense but why even waste part of the poll on the Star Wars prequels? Sure they have their fans but you could have put other things there.

Changed it to Evil Dead.

Anyways to answer the question : I can't answer the question!

I've seen some of these but only a couple of movies or too. The only ones that are semi-fresh in my mind are Star Wars, The Godfather, and The Dark Knight trilogies (and those are all from years back, some probably 5 years back).

However I'm kind of thankful this topic was made, because I've been going through movies and I might now use this to check out some classic trilogies

Lord of the Rings for me, easily. Most trilogies have at least one movie that is a lot weaker than the best. The "worst" of LotR is still amazing. And it's holding up really well due to its focus on practical effects and smart angle and perspective tricks in shooting.