Hey guys, there was a point in time (1 yr ago) when I wanted the very best portable, so I didn't have to buy a desktop amp. Back then I would absolutely have to have a P-51 Mustang no matter the cost. Now I realize the advantages of the desktop amps, to the degree that all I need is a great portable for when I am away from my home rig, but it can be #1 or #10, and I'd be happy. (unless there was no home rig to come home to).
I can tell you that any of the amps Skylab has ranked in the #1-10 place (or even #11 based on other's feedback) are probably fantastic and "good enough". I own a #3, #4, #7 and #8 ranked amp, and have heard the other amps that were tied for #3 and #7. While my preferences in sound may be slightly different, I understand completely how he came up with his rank. Most of them sound extremely good or very good, but some do some things better than others, and few do EVERYTHING right.
I think the 4 amps that Skylab has placed in the #1 and #2 spot (with ties) are kept separate with a blank line from the rest of the amps because they are the ones he feels do just about everything right. But, he hasn't tried every headphones with them, and there will be some that don't sound their best with those amps. So, you may buy an amp high on his list, and not like it and wonder how he could have ranked it so high, or find an amp that is amazing and wonder why he didn't make it #3. I say keep an open mind and don't be afraid to try something elsewhere in the list other than the top, because there may be a synergy with your headphone that brings out the best in the amp.
I try to make it a point to listen to them with most of my full size and IEM headphones, portable or not - but that doesn't always make a lot of sense with headphones that would be difficult to use portably. When are you likely to see someone using an ipod and amp with the Denon D5000 or HD600 out and about, on the bus or library? I do it because they might be used in the hotel room or at work with the portable amp, and I have been only interested in amps with built-in DAC for that purpose. For non-DAC amps, using only portable headphones for the review makes sense (and we have plenty of P-51 reviews with Meridian CDP and Sony R-10 already out there already).
So, Skylab has certain tastes or reasons for wanting to review certain products, and I have mine, and others will have their own reasons. I'm not terribly excited about reviewing an iQube (no DAC) and turned down the offer for a loaner a while ago, and Skylab doesn't want to review another iBasso - we just have to accept those things and move on.
Cheers, and thanks Skylab!