My mom uses a mixture of collard greens, kale. However, I think an updated version might include spigarello. This year, she used ham hocks and bacon, and tabasco.

The vinegar sounds like an idea for next year!

Chop and sweat an onion & 1 clove garlic. Add a generous pinches of red chile flake. Add in a few smoked ham hocks & collards. Barely cover in chicken broth. Cook until meat falls off bone. As others said, adjust heat taste with tabasco. I don't usually add extra vinegar beyond the tabasco, though. Just personal taste preference.

(I always make this if I've done a holiday ham. Don't work too hard at getting all the meat off the bone and let it melt away in your greens. A honey or maple glazed ham is particularly nice.)

Good call on the vinegar folks. Tabasco and most Louisiana style hot sauces use vinegar as a foundation. So you can tweak the balance to your taste.

I often cook mine with some vinegar as well. The Lee brothers have a few good recipes in their book. For a change, I really like this:
http://www.food52.com/recipes/7474_toasted_moong_dal_with_collards

Totally agree with pierino. Another idea: Instead of (or in addition to) Tabasco, sprinkle a little vinegar (try sherry vinegar if you have it) on top when you serve it.

Bacon. Trim the collard leaves from the stems, stack them up and slice very, very thinly across the grain. Brown the bacon, discard the fat (most of it anyway), transfer to a pot you can simmer on the stovetop. Add the collards and some liquid (water or broth). Simmer slowly for about one hour. Collards really need to get "hammered" to cook through. Finish with salt and pepper and some Tabasco.