ETransatlantic flights offer what United calls Polaris (business) class. All flights, regardless of aircraft type, will have Polaris service. Some aircraft will also have Polaris seats.

Polaris service includes access to the Polaris lounge (available in the US at certain airports). It’s United’s best asset. Onboard service is ok. Average food. Below average drinks. Some airports have an arrivals lounge if you are terminating there (think showers and breakfast).

All planes have lie-flat seats. The Polaris seats are more private whereas the alternative seats aren’t.

You will get a lot more specifics if you post more info about your route.