The latest study from the cellular-data research body Opensignal reports that Verizon has the most widespread 4G services in the US (at 94.8% coverage). However, T-Mobile was associated with the best upload and download experiences on the same network. This new report also claims that all carriers included are improving in terms of these mobile download speeds.
https://www.notebookcheck.net/T-Mobile-has-the-fastest-4G-in-the-US-although-Verizon-has-the-best-coverage-latest-research.427785.0.html