Crystals Are Better For Initial Calibration Accuracy And Temperature Stability.

Resonators Are Typically 0.3% Accurate And 0.1% Temperature Stability, While Crystals Are 0.005% On Both Accounts. In Most Applications, The Resonator Is Adequate However.

I Have One Project That Has Timers Running Up To 24 Hour Range And Temperature Exposure Of 0-90 Degrees Farenheit And Used A Crystal For Stability.

Most Projects I Design Are Ok With The Internal Rc Clock.