candela It's been a while, but I recall those active Rokit speakers they have on display at Guitar Center giving me a bit of a headache. Might be the volume is too loud or the treble is over-amplified. It's been a while though.
Also I have experienced iLoud speakers that seem to pick up a lot of interference and just seem inherently noisy, but perhaps that can be attributed to other factors like the cables or the system it was connected to. Everything in the chain matters, obviously. That might be one off experiences.
I'm all for flat response though!
I recently assembled a microphone and the seeming lack of any inherent noise at all floored me. I imagine the same would be possible with a speaker too.
Given the choice between headphones and speakers, I would personally pick speakers. I have heard good things about Adam and honestly iLoud as well. Have you considered Yamaha? They have the HS series for example — they might have speakers uniquely designed for instruments?
And if using headphones, I have had excellent experience with the open-back headphones... the experience can be uncannily realistic.