Gain Bandwidth Product on an op-amp
If you need high frequency accurate_gain, then pick the faster.

If you need low distortion at high frequency, where the difference between Vin+ and Vin- (often pins 3 and 2 on older opamps) determines the distortion because of hyperbolic_tanh curves of bipolar differential_pair input response, then pick the faster.


Fundamentally the Vout is Avol * VIN, and VIN = (VIn+ - Vin-); as Avol drops with the UGBW plot 1:1 with frequency, the VIN has to increase, to sustain the same output voltage; this requires MORE voltage across the diffpair bases, and you are guaranteed MORE distortion.

If you need the inductive Zout of opamps for some oscillatory behavior, and you need how the opamp converts the Rout into the inductive behaivior, at higher frequencies [some opamps are characterized well past 100MHz with such Zout] then pick the faster.

Notice the UGBW makes NO PROMISES about the smoothness of settling, which is important for quick response to the switching of input channels, such as switching sensors in a telemetry system. Settling depends on phase margins, and on the width of the input VIN response region; emitter degeneration is the way to widen the input response region for bipolars; for FETs, the designer has Width and Length and Idrain as controllable params. For fun, examine the schematic of UA715 opamp from Fairchild. The emitter degeneration, and the collector cascoding, are key circuit methods to achieve fast settling. The collector cascading will seriously reduce the input capacitance, speeding up the time constant of the Vin- pin settling.