Really delicious roast beef?

I’ve been happily vegetarian for about 25 years, so I’m a real neophyte about cooking meat. But, I’m having guests for Christmas, and I want to serve them roast beef (I’ll make a lentil dish for myself).

What cut of meat should I buy?

Do you recommend rubbing or pouring anything on the outside of the roast?

How do you do the actual roasting? I’ve tried to research this, but there’s no consensus. Some recipes say to use a low temperature for a long time; others say that this slow-roast method has a rubbery outcome, and that I should use a very high heat.

Please help me, my fellow Flutherers! Thank you.