While I've not owned or even heard the AK70, I have owned the AK Jr, AK100II, and currently own the AK120II. I also own the shure SE535. I would say the AK70 beats out the AK Jr on everything except price and form factor. The Jr's UI is rather laggy and comparatively unresponsive. If you have a larger library, it's aggravating to see the player struggle to register your swipes and to take seconds longer to load albums and artwork. The overall UI isn't as well thought out as the one used on Astell & Kerns' other DAPs. Plus, the AK70 offers wifi which is useful if you like to stream music and convenient for firmware updates. In terms of sound, I personally prefer the sound signature of the AK DAPs that utilize the CS4398 DAC chip. That's not to say that the AK Jr doesn't sound good to me, but I feel as though it is a little too warm for my personal taste (especially with the SE535) and is not as resolving as the other players. As the AK70 has the same DAC as the AK 100II I have to go under the assumptions that they have a very similar sound. In my opinion, if size isn't a factor and you can get them for a similar price (or if price isn't an issue) then I would feel very confident in recommending the AK70 to you. Good luck and let us know which one you go with in the appropriate threads! I know it can definitely be a bit crazy when you first get into it but my recommendation is read as much of the forums as possible to get a better understanding of the landscape and over time you'll start to realize your own preferences and the options start to narrow a bit.
