I'd go with a carnivorous plant terrarium. But that's just because I can't keep an orchid alive to save my life. Once I bring them home, they slowly suffer a prolonged and miserable death under my care. I am much more successful with my CPs.
“The day the power of love overrules the love of power, the world will know peace.”
― Mahatma Gandhi
Pitcher plants (Sarracenia) and venus fly traps (Dionaea muscipula) don't usually make good terrarium plants, they don't require the level of humidity common with terrariums and the lack of drainage may cause them problems.
For terrariums I'd suggest one of a few genera of carnivorous plants:
Utricularia (bladderworts, carnivorous action is underground, some aquatic species available)
I do know of people who have successfully kept Sarracenia and Dionaea muscipula in terrariums but they both have a winter dormancy period that is critical to their long term health, this cannot usually be maintained in a terrarium environment. Some species of Drosera and Pinguicula have a dormancy period (or "dry rest" period) too but if you choose tropical Drosera or warm temperate Pinguicula (and do adequate research into each species) you'll have no problems. Mexican Pinguicula are a no-go for terrariums, regardless of some of them loving humidity or high temperatures as they are prone to rot and have a winter rest period that must be respected.
If I can help at all with carnivorous plants you choose (should you go for it) then by all means please let me know :) I wish you the best of luck and hope you'll post photos!
"There will come a time when three words uttered with charity and meekness shall receive a far more blessed reward than three thousand volumes written with disdainful sharpness of wit."