"Which do you like better, pork or beef?"
Nothing. A real translation would be: Which do you like, pork or beef? That's what I think
のほうが好きwould have been better. That confused me to, especially since they introduced it in the last lesson.
It feels like something is missing between "Butaniku to gyūniku" and "dochira ga suki desu ka". Is there something that would fit? "Wa" perhaps?
The sentence is correct. が in どちらが好きですか？is what you are looking for.
You could say 豚肉と牛肉とどちらがすきですか. I've seen it both with and without that intermediate particle. I'm a little fuzzy as to its purpose but I just asked my tutor about it.
When the particle と is used as "and", it lists thing exhaustively, i.e. there is nothing else to consider. If you were to say 豚肉と牛肉が好き, it would mean "I like pork and beef." There is no implication that you might like anything else.
Another particle (don't worry if you don't know it yet), や, lists things inexhaustively, i.e. "Things like X and Y and ~ … " So, 豚肉や牛肉が好き would mean, "I like things like pork and beef." It implies that you like other things as well.
To summarise, と refers to/adds things to an exhaustive list. や refers to/adds things to an inexhaustive list.
I'm not fuzzy on the meaning of the particles や and と, but in 牛肉と豚肉と、どちらがいいですか？the secondと isn't always added and i was curious why. (The answer turned out to be that it's more polite.)