[Chumbalaya]

There is no best Elites choice, it depends on how your army is set up.

Generally, though, Orks have a huge lack of reliable anti-tank. For this reason, Lootas stand out as your best option for busting up armor below AV14. They're great support for just about any list and taking 2-3 big units is almost always a good idea. It's about as close to being the best as it gets.

It's also much cheaper to convert Lootas yourself by taking normal Boyz and adding weapons from other ranges (see if some of your local group have a stockpile of random heavy weapons they no longer use).

Nob Bikers if you want your opponents to hate you and your overpoweredness.

 

[Chumbalaya]

Take nob bikers I have never defeat my friends ork list do to the simple fact he runs a 9 man squad of them with a warboss right down the middle of the field. (Still I have never really lost to him either since we usually kill each other off almost to the man).

Nob Bikers should be Troops if there's a Warboss around. Even then, the unit costs well over 600 points when tricked out and is the classic deathstar. It can destroy precisely 1 unit at a time (multi-assaults are possible, so spread out and layer your defenses) and suffers against fast moving vehicles (hit on 6's FTL) and anything with a Storm Shield. Use a layered defense with fast moving vehicles, tank shock them into bad positions, and drop S8+ shots on them all day. Nob Bikers aren't hard to beat if you play it smart.