The ones I'd most recommend, in my order of preference, are:
FFVI
FFIX
FFXII
FFIV
FFV
You can also throw FF Tactics in there somewhere though it's an SRPG outside the main series, but still one of the best entries out there. The PSP release in particular had a much better translation than the original though the original isn't unplayable by any stretch.'
Outside of those entries I consider the rest of the series to be of varying quality. Anywhere from average (FFVII. Yeah, I said it) to terrible (FFVIII). The original 3 games aren't terrible either in the context of when they were made, but they've certainly aged far worse than most of the others.
FFVI
FFIX
FFXII
FFIV
FFV
You can also throw FF Tactics in there somewhere though it's an SRPG outside the main series, but still one of the best entries out there. The PSP release in particular had a much better translation than the original though the original isn't unplayable by any stretch.'
Outside of those entries I consider the rest of the series to be of varying quality. Anywhere from average (FFVII. Yeah, I said it) to terrible (FFVIII). The original 3 games aren't terrible either in the context of when they were made, but they've certainly aged far worse than most of the others.