I wonder, what's the best oscillator scheme to use with watch crystals(32kHz) to get optimal stability & precision? (provided that temperature is stable, digital correction is out of this topic).

Typical solution is pierce oscillator, but what's the optimal swing/voltage?
I have a feeling that sine-wave generator should put less stress on the crystal.

So, what's the best & less stressful oscillator scheme for watch crystals?