Best Viet coffee I made was using Lavazza in the red/blue bags. It's a blend of arabica and robusta. This was many years ago though, so it's possible the newer beans have a different profile. I just remember I got pretty great results with this, after trying several different beans. Brew low temp, around 80 C
You really need some robusta in there, but I would not want 100%. Trung Nguyen is a blend. I tried other viet brands and they was fine too, just that it's easy and cheap enough to get Lavazza. Cafe du monde has chicory added, so it will be a different drink.