I'm currently without a monitoring system I fully trust. Have been intending to check out a pair of Neumann monitors since last winter, but have yet to commit. I plan to use their calibration kit to hopefully enable an improved degree of monitoring consistency when moving between various locations.
I currently use Sennheiser HD650 and Senn HD600 headphones for the most part, both of which I use for casual listening as well, and the car via analog line-in. Biggest problem for me is getting sufficient insight into the low end. The Senns are a bit overly accommodating of excessive bottom. I know them well and trust them for critical listening from the midrange on up, but they really like a touch of excessive low frequency emphasis in the source. Not sure if I'd really call them "overly lean" sounding on balanced material, but "overly accommodating of excessive bottom" seems a good description. When playing material straight off the recorder made with my current rig that includes a pair of relatively wide-spaced omnis in addition to other directional mics the Senns are just about perfect. But I cannot trust making low end EQ decisions that correctly translate elsewhere.
My car stereo is an alternate check, but less trustworthy than the Senns. It has the opposite problem in being an overachiever down there, not just with an elevated low frequency response, but something of an unfortunate Q hump. Unless the material was overly lean to start with it generally requires a decent amount of low shelf tone control reduction simply for normal radio/CD/whatever listening. Stuff that sounds great on the Senns requires fully cranked low shelf reduction in the car and even then it's usually still too much.
My folks place has a Bose sat-sub system I plug into, which has response issues similar to the car, just less so. Its another good check, but similarly unreliable for mix decisions.
I didn't have the same degree of low end translation problems back when I had a multichannel setup based around 3 floor standing B&W802M across the front, optimally arranged in the room. And my long term experience with that system instilled a strong desire to get everything from the low-mids on down carefully dialed in correctly and not just lopped off, particularly with live music recordings. That system is currently in storage.