Best sounding current production headphones with *no* sound leakage?

I'm pretty sure it's Ultrasone Edition 8 however I haven't tried many of today's top tier closed 'phones. Edition 8 improved over Edition 9 a bit IMHO.

The Stax 4070 Monitors are without question (IMO) the best closed headphones available, sometimes I even prefer them over the 007's, they are that good they look big but I find them extremely comfortable, I wear them daily for hours...

I also have the ed.8, they are the best non-vintage closed dynamic that I know of, they're compact to the point that sometimes I walk with them and beautifully built (imo the 4070's are at the same level of craftsmanship or a bit higher), but the sound as good as it is, does not approximate the satisfaction I get with the 4070's. The ed.8 seem somehow opaque, slower, boomy and closed in comparison.

I much prefer the W5000 over the Ed8 due to its combination of superior detail retrieval, speed, soundstage, and imaging. The bass of the Ed8 does extend much lower than the W5000 though.

If the W5000 is like the W1000, though, it probably leaks some sound, much like the excellent line of Denon woodies.

The best closed headphone I've heard with zero leakage is the Shure SRH840 (I've never tried the 4070 mentioned above - I'm sure it's fantastic but would probably be way over budget)

Just read the review here First Listen: Audio-Technica ATH-W5000 "Raffinato" Headphones | AVguide

But yes question if it´s as loose fitting as the A900 which leaked like crazy.

Edition 8 isolate like a champ a LOT better then Pro 900/DT 770 Pro but that seem to hurt the soundstage too. A combination with the small ear cups, treble roll off and mid bass/mid range boost I suspect too. They certainly do have a closed signature. Big disappointment after coming from the Pro 900 in that regard. Lack speed since the air can´t escape I suppose and smallish ear cups? Longer decay yet they feel more aggressively damped then the 900. You won´t get any resonances from the cups which benefit the bass some. KeeS mod (don´t worry anyone can do it and it´s less then 15$) helps a lot on that one though

Pro 900 isolate about as good as the DT 770 Pro and are certainly a couple of tiers above. Already the Pro 750 blew me away. Had the DT 770 Pro prior to that one. Pro 900 beats the Ed 8 in quite a few areas particularly if I put my audiophile ears on and totally disregard price tag and looks . Higher resolution, better attack and shorter decays except for the about 3x wider soundstage and much better instrument separation as a result. I get the feel the Ed 8 is more of a fun headphone made for portable use soft and polite with good looks and superb isolation designed to perform good on lesser sources rather then scale. They do perform based on that but on a serious home system they are still VERY musical with a really nice tone that is easy to fall in love with.

DX 1000 I also had quite fun with so they are huge and you better not be afraid of looking like a teletubbie among your collegues. Though they are very picky on what works on them and what not at least for me. Doesn´t quite have the isolation of the 770/900 but probably good enough. For classical, jazz, opera I was happy most of the time. Sure they are coloured but WHAT colour for that genre . Soundstage size equal to the Pro 900. You will hear the sound bounching around in the wooden earcup on them so it depends if you like that or not. I thought it was really cool in the beginning but then I started to just hear sound in wooden tin cans. But I suppose I am quite anal about soundstaging.

Edition 8 do offer a 35 return warranty at least from the shop I bought them from. But better not try them out unless you are really willing to spend that much. Can be quite hard to let go