Ok just to sum it up
Marantz MPH-2 (on sale for $40 if you get very lucky + brainwavz angled memory foam pads $25) => best value (detailed, great controlled bass, pretty decent mids)
note: MPH-2 without those pads is overly boomy, bass bleeds into mids, V shape. not very good. note that MPH-2 is the same as lynx and akai which sell for $25 to $35 do not overpay.
Superlux 668B (~$40) + Brainwavz XL round pads ~ $25 + ZMF pilot pads $30) => 2nd best value (decent bass, decent mid, decent highs, detailed airy sound). it is light and you can abuse it as much as you want just does not break. i have stepped on it and nothing. a lot of burn in necessary.
note: without these pads very uncomfortable.
Monoprice Retro (~25 bucks) awful for any music with vocals, folk, classic rock, just good for instrumental modern bassy electronic music. overly bassy with dreadful thin sounding mid range. uncomfortable with stock pads. not only i had to add ear pads, i also had to mod the headband with 3m stick on real leather pads and not worth it. not recommended although the headband mechanism which is similar to AKG 701 is the best that there is. it just conforms to head of any size or shape but the headband is cheap awful plastic instead of nice feeling leather or fabric. so it is a weird combination of good design and bad material. does not feel good.
The Sonus faber Pryma is not recommended if you just consider sound. it does not sound any better than the marantz or superlux after 50 hours of burn in. not very comfortable either even though it is light.
the hifiman HE400i is the opposite of the HD6XX's silky smooth and relaxed presentation. it has high energy high freq but it also has sub bass. at $150 these days and after 100 hours of burn in it is absolutely recommended. it is a very good example of planar sound on the cheap. it is not bassy but it has sub bass. for me it was eye opening. 100% recommended at the price that is sells now ~150. thank you hifiman for selling it at this price even though it has documented QC problems still buy it and when it breaks just email hifiman and get the parts and replace them yourself.
audeze lcd-2 classic is all the planar anyone ever needs.
Hd599 and Audeze LCD-2 classic, marantz MPH-2 and superlux are the ones that i decided to keep, even though Hifiman HE400i and monolith M1060 are better values than Audeze i just had to have the world class bass with good mids that classic has and i just wanted to own an audeze.
AGD R2R11 is the bargain of the fucking century and chances are there will be no more centuries after this one so dont make babies instead buy Audio-GD R2R11.