Both work very well it depends on how well you can attend the BBQ. any BBQ will need careful attendance and temperature adjustment to prevent flare up or burning. An oven is easier since it is just set and timed.

Personally either way I prefer an oil rub like this one for optimal flavor:

1/4 cup Olive oil

2 tablespoons each of rosemary, thyme and parsley, crushed black pepper

2 cloves of minced garlic

1 Tablespoon kosher salt

Combine and rub well over entire roast.