Is a high FPS number always better?

No. A high FPS number on the box usually comes from the lightest, cheapest alloy pellet a manufacturer can find, and those pellets often have terrible accuracy.

Heavier lead pellets at lower velocity routinely deliver more energy at the target, more accuracy, and less wind drift. Above roughly 1,100 FPS, lead pellets often turn supersonic and become inaccurate due to transonic instability. Chase accuracy and FPE, not the headline FPS.