"What do you prefer? Tea?"
Translation:Beth sy'n well gyda ti? Te?
I have a feeling you could use gen ti (informal), or gennych chi/gynnoch chi and gyda chi (all formal) in place of gyda ti (informal), in this sentence and it would mean the same thing. Choice, I suppose, is down to formality and dialect (northern or southern usage). Not sure about gennoch chi though as I have not come across that word?
For 'prefer', (g)well is used, not (g)orau.
The gwell form is usually taught on beginners' courses, but gorau is used by some for "prefer" - Beth sy orau gen ti? instead of Beth sy'n well gen ti? and such like. Geiriadur yr Academi even mentions it in its entry for "prefer" in the example sentence "He prefers this one": Hwn yw'r gorau ganddo, Hwn sydd orau ganddo.
See shwmae's comment above. What is happening is that gorau (best) is being used as an adverb, and this means that it gets mutated to orau. In that form and usage there is no need for the linking 'n/yn:
- Te sy orau gyda fi - I prefer tea
That form is used in the wild, but the sy'n well pattern is perhaps more common and is the pattern taught on Welsh for Adults courses in Wales: