VI and IX are my favorites of the two eras I guess you can call them (9 being my overall in the series). I feel like the characters in both of these games are so strong. Also, 9 is charming as hell.
If you can only get two, buy VIII and IX. VII has not aged very well, graphics or gameplay. But whatever you do, do NOT buy V or VI. They are horrendous ports with incredible loading times.
Eh, yeah the translation is pretty haphazard for 5, but I don't recall any glaring load times. Then again I'm probably more tolerant towards that stuff then most people. Also, that JOB SYSTEM.