United aircraft have one of three different internet systems. United Express aircraft have a forth, GoGo. Performance and coverage will be different depending on which system your airplane has.

https://www.united.com/ual/en/us/fly...ight/wifi.html

I think the ViaSat is the fastest and most stable. Thales has good speed but seems to be a bit more temperamental and has the smallest coverage area. Panasonic has the coverage for the Global flights but I don't have any experience using it. Pre-pandemic, they identified some issues with Panasonic and upgraded the airborne hardware to improve performance and reliability. GoGo, on UX, is a ground-based system, not satellite. All new 737 deliveries will have the ViaSat system.