UPDATE02
For better or worse I am now trialing Onspace (which is now out of Beta before you ask). So far it feels "slick but not easy", but I am a total newbie so probably doing everything all wrong! One of the worst things about Onspace IMHO, is the way free rotation works in that unlike Fusion 360 or 123D Design or Sketchup you do not orbit around a vertical axis. So very quickly as you orbit any vertical lines are no longer vertical on the screen and this can quickly make you feel seasick if you're me!
I have been beating them up about it, because to me what Fusion does is clearly much better, but apparently some of their current users think that they prefer it like that...

On the other hand I do quite like the way Onspace shows you the parametric constraints that are in place. More later...