One more important note on the AK120. Although I haven't heard the new unit yet, I have read that the ability to play with seamless track breaks(continuous play without annoying pauses) is now a reality with the AK120. The AK100 may have a firmware upgrade available to fix it's issue.
In any case this is a really minor issue, the important aspect to these units is the incredible sound playback there capable of producing. Currently I don't think there's a better portable MP3 player on the planet.
It's only other real competitors(please do add more if you know of others fellow Head-fi's) are the Fiio X3 and the Ibasso DX50 and Ibasso DX100(this unit is actually more expensive than the Astell & Kern AK100 but it's competitor the AK120 is markedly more expensive), the only competitors. The main advantage of choosing one of these three alternative players is the price factor, however all of them have inferior design construction to the Astell & Kern. Also from reviews I've been checking out on them, none of them can match the Astell & Kern for clarity and crispness(I know a wild word to put to you) of sound.
Having said all of this, the important words here are 'quality of sound'. This in itself is a very personal and debatable topic(one reason I'm always skeptical of reviews that rave about products), the only real way to decide between the players and be 100% sure of your investment, would be to go into a quality audio shop with your favourite headphones you'll be using on the unit you decide upon and try them all out. The ultimate decider will always be your very own ears. Your ears are unique to you. You will interpret sound differently to everyone else. What one reviewer declares is the next best thing since slice bread, may not be what you imagined it would be or even could be. So when making an investment of this magnitude for a portable piece of HiFi kit, you owe it to yourself to try before you buy where ever possible. You'll be glad you did.