Navel is the best cut of beef to make pastrami from. It yields nice slices suitable for sandwiches. The fat content was perfect for commercial use when the pastrami would be put in the steambox in the morning and pulled out as need to slice for sandwiches in the deli. At home or in restaurants that don’t use a steambox/table and heat with a microwave or grill it is extremely fatty and greasy.
A less fatty cut that can be used is shoulder, but it is tough to chew if not sliced extremely thin.
I cure my own meats in my backyard smokehouse and always use navel for pastrami.