The triangle is easy so long as you're en excellent counter
i've played trumpet before, it is hard. im not much of a brass player.
but ive read trumpet is pretty easy to start with, and clarinet and flute are easy to start with. trying to become a master at it is what's hard.
ALL INSTRUMENTS ARE DIFFICULT. but there are some that may be a little more difficult. and research the most difficult instrument, i guarantee oboe will be listed.