As solderdude was intimating, you don't have to really think about planars vs dynamic drivers, it ultimately comes down to frequency response & distortion.
If you're not specifically after the qualities of a closed back headphone, ie sound isolation from your environment - if you're environment is noisy or you don't want people in the same room hearing your music over your headphones, then open backed headphones arguably can offer better benefits to sound quality on the whole vs closed backs. So if you're new to headphones & don't have a decent pair yet, then I'd go open backed if sound isolation is not important to you. You saw my earlier recommendation re HD560s. If you at that point (after EQ) then enjoy the headphone experience you may feel nothing is lacking & then you're done. Alternatively after doing all that you might feel headphone listening is still totally inadequate at which point you'd probably conclude that it is indeed so, and you will have saved yourself $2000 on an expensive experiment, and you won't buy headphones ever again. Finally as the last possible scenario, if you enjoy the EQ'd HD560s and it makes you think headphone listening worthwhile & good, but you feel there's still something lacking in the sound quality, then I'd advise you to jump straight from that to the E3 as I don't think there's much worthiness flapping about in the middle. When I talk about "sound quality" in my previous sentence I'm referring to everything else apart from soundstage, you shouldn't expect to get anymore significantly speaker like soundstage from the E3 than the EQ'd HD560s - I think it's important to understand the limitations of headphones in this respect, and whilst soundstage can be improved from headphone to headphone it's never quite the same as listening to speakers so you shouldn't expect that.
For instance to put some of what I say in previous paragraph into perspective, my best headphones for me after EQ are HD800 / K702 / HD560s, and there's not massive differences in overall quality of experience between them eventhough they all sound a bit different after EQ and all have slightly different soundstage properties and some do better bass or better treble than others - but it's not like there's a massive difference in overall quality of experience. So from my point of view I'm done with headphone purchasing, and if I ever do buy headphones in the future I'm not gonna flap around in the middle (eventhough HD800 is not a middle tier headphone & which in itself leads me to think headphones can only get so good) - the only thing I'd left to experience from a measured excellence position would be Dan Clark E3 in my eyes (Stealth has too much on head variation for my liking). Even then I don't think there is much incremental difference in quality that can be achieved, I'm not that convinced, but if I ever did buy another headphone I'd go straight to the top as I feel I've experimented with many headphones & many different EQ's and already maxed out the middle ground (& top tier too to some extent if you think HD800). But, might be a bit rash for you to go straight to the top, because you're not even sure you like headphone listening, hence refer to my previous paragraph.
