Sine wave PWM: which is better analog or digital?
i don't know if it's suitable for 50 hz operation


A bubba oscillator is just a phase shift oscillator and so can be made to work at any frequency within reason. It uses op-amps to provide low-loading of the phase shift circuits so that the frequency of operation is more mathematically predictable. However it's very wasteful in its use of op-amps.

Like the Wien Bridge oscillator there is no natural amplitude stabilization so you find that the gain has to be dynamically controlled so, when you say: -


  I know that the 4-section bubba oscillator has good stability


This isn't exactly true because it trades distortion for amplitude stability.

If you want a decent sine wave oscillator I would consider making one that has a tight bandwidth (high Q) filter and in-built amplitude control like this one from Elliot Sound Products: -



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