FFVII may have many bits of dodgy translation, but when it's good, it's good. The characters' voices are more individualised - in general, they each have a distinctive tone and style which makes them stand out, and adds a great deal of colour. In FFVI, however, it's often pretty generic. Most of Terra's lines are in a style identical to that of Celes or Locke; the only really unique voices belong to Gau, Umaro, and occasionally Mog. Cyan has the occasional token word of "olde worlde" language to make him sound grandiose, but it doesn't really fit - it's like something that's been deliberately shoehorned into an otherwise mundane sentence.
Basically, FFVI has a superior degree of consistency to its translation, while FFVII reaches greater heights with the way it gives unique voices to the main characters. As a result, FFVII's profound moments are further enhanced - like Cid's "someone's gotta defend the Planet, and that someone is us" speech. There's plenty of similar dialogue in FFVI, but it's usually so generic it doesn't stand out.