I'll describe my impressions in sequence of acquisition of the headphone.
Grado SR60e (Sept '15):
The 60e where my entrance to good headphones. For one, they are really affordable, they have lush mids and loads of energetic treble that makes this headphone extremely well suited for the music styles I prefer: rock, alternative. The treble can be a bit overbearing at times though. After a while I did notice the drawbacks of these cans; they are lacking in the bass department, therefore not a good fit for electronic music styles, such as Daft Punk. Comfort wise they weren't the greatest either. I have tried the S-cush, L-cush and G-cush pads(bowl pads). On the SR60e I like the L-cush the most, since I find the bass to be be muddy and overbearing with the bowl pads. The comfort is great with bowl pads though. The cable is not removable and that sucked as well. This eventually led to me looking into other headphones with a different sound signature. I wanted at least one neutral can and one that excels in the bass department.
After a decent amount of research I found a decent deal on a used pair of X2's since there was a whole 'glued pads' debacle at the moment I was looking into them.
Philips Fidelio X2 (Dec '15):
I bought the Fidelio X2 to supplement the Grado and to shine in the electronic music department. The overall sound signature on the Fidelio X2’S is full and well balanced with a small hump in the bass region. Although the X2’s are a full sounding headphone it still offers great clarity and details and there’s no sign of muddiness in the presentation.
The bass is probably the first thing I noticed when listening to the X2’s. It’s the first thing that sprung to mind and impactful for an open headphone. The bass excels in the lower notes and rarely does it get boomy and leaks into the midrange. The bass has very good layering and feels well controlled and integrated with the rest of the sound. I really enjoy this headphone for movies, gaming and music that needs well developed bass.
After a while I was intrigued by the existence of DAC's and amps, which led to the following acquisition:
Sennheiser HD600 (Jan '16):
This headphone is being called the king of neutrality and one of the best price/quality combinations in the current headphone offering. This is a classic for a good reason, the HD600 creates a very convincing natural sound. For good reason it is my reference headphone, and at the same time a perfect allrounder for multiple hour long listening sessions. Comfortable, just the right clamp force and a decent cable, although a bit on the long side. I bought a better looking replacement which fits better for my desktop home listening sessions on ebay in the meantime. The lows are definitely less compared to the X2, but so well defined and in good quality I don't feel like I am missing out much.
Schiit Modi2u & Vali2 (end of Jan '16) in combination:
The Vali2 is more than sufficient to drive the HD600, and I like how you can use tubes to finetune the sound. The differences are not mind blowing but subtle, so don't expect too much. The HD600 needs sufficient amping, especially for the low end. The impedance can reach almost 500 ohms in the lower frequencies, according to the measurements by Innerfidelity. There is discussion on how much this influences sound it endless. According to audiobot, peak SPL is 127 dB with a damping factor of 52.9 and 255.8.
Modded Grado SR60e with GS1000 style wooden cups Magnum V6 drivers (13 May 2016):
For my impressions on this setup you can read the extensive story here. But I'll give my more recent impression here as well (I bought the drivers and cups in April/May '16): The Symphones drivers are described as slightly u-shaped. They are fairly neutral with a slight emphasis on the high and low end. They make the Woody as good as a an allrounder to me as the HD600, with the benefit of being fairly sensitive/efficient and thus not needing an amp to sound good.
Note: Sadly you will not able to purchase these drivers anymore since Rhydon from symphones.com has released the Magnum V7 drivers. Since I have no personal experience with these drivers I cannot express anything about them.
Sennheiser HD800 (Oct '16)
You can read my detailed impressions here
In short, the HD800 is one, if not the best headphone I have ever heard. The presentation is wide and spacious, compared to the intimate presentation of the HD600. The HD800 presents details in the music in a effortless listening experience, while with the HD600 you need to focus to pick up the finer details.
If it is worth the purchase, that's up to you. I believe it was, but I might have reached a point in life I need to say goodbye to one of the above mentioned.
In conclusion
Which headphone do I prefer most?
This question is very difficult to answer, it really depends on the type of music I would be listening too at the time. For more bassy EDM, the Fidelio X2 is king. For classic, the HD800. For allround performance the HD600 or the Magnum GS1000. It really depends on what I want at the time.