My vote goes to Logic's ES1. It has a clean interface and has all the basisc and nothing more so you won't get distracted. As an example: it doesn't have HP-filters which would only have made things more complicated. Also a sub osc, giving you a short piece of knowledge about sounddesign. But the best thing (and rather unique I think) are the 2 doubled sliders:
- one for the velocity impact on the filter cut off,
- and another one for the velocity impact on the amp.
Most synths have a single knob for velocity sensitivity together with another knob for the impact for the envelop on the cut-off. Then a single slider with a min and a max makes things much easier to understand IMO.

Also a big fan of Motu's Modulo. There is a lot to modulate over here but Motu managed to show it in a very organized and easy to understand way. Tabs for LFO and envelopes and instead of a modulation matrix they gave that one tabs as well making it easier to understand for newbies. After all a modulation matrix is more complicated than tabs where you can select amounts for destinations. Wish there was something like this as an AU.
(the interface flaw they made btw is the LP12 LP24 BP HP section, just like the LFO and ENV tabs it suggest they can all be active at the same time)




