I’ve just re-worked an old post to better display some comparisons. It’s still in the Sandbox at the moment, so not entirely finished yet, but you might still find it useful. 
We’ve got the Classic and the Premium, and Mrs Chimp thinks they’re both excellent. 
The Premium does have a few swish extra features in the Smart Silence and Autopilot, plus 4 extra intensities (though not all jammed in at the top end ), but the Classic is still pretty solid. I think, budget dependant, I’d go with one of the ones with more intensities and a bigger battery.