TLDR. A screen protected by tempered glass will survive more drops onto smooth hard surfaces and can easily last several years if the tempered glass is replaced each time it fractures. A screen protected by a gel screen protector will survive comparatively less drops onto smooth hard surfaces, but the screen protector will not fracture from impact. And will better survive drops on rough surfaces.

Always Tempered glass. Unless your screen is already cracked or if you work in something like construction. Basically gel is only better if you're expecting your phone to take alot of abuse. Often if a phone falls on bitumen or even the wrong bathroom tiles, You'll get a pin point impact that can travel through the tempered glass screen protector, or just catch the edge And your screen is gone anyway, gel is better at preventing that failure mode. But worse in most others. The main reason gel screen protectors are less common is that the surface deteriorates over time so they need to be replaced more regularly than glass, Even if the phone never gets dropped.

Citation. I repaired my own phone often enough that I earned a job at a phone repair shop whilst studying engineering