The classic question. Short answer: ModernFix gives more FPS, OptiFine has more visual features. Many players run both.
ModernFix typically wins by 20-40% in raw FPS on the same hardware.
For performance pick ModernFix. For shaders and zoom, add OptiFine on top — they work together.
Related: Home (/), 1.20.1 (/1.20.1/), 1.19.2 (/1.19.2/), 1.18.2 (/1.18.2/), 1.16.5 (/1.16.5/)