I would rate IV at the bottom for pioneering the "cinematic game", but I have to admit that it's a fairly well put-together game, if boring and linear with zero replayability. Unlike II and III, which are broken on a basic level. Between II and III, I actually think I prefer II since it respects your time better than III with its retarded as shit gimmick dungeons. II also has a better story. I still think II deserves at least 3/4 of the hate it gets, though.
V is indubitably king of classic FFs and one of the best JRPGs ever made with regards to replayability and versatility. VI is quite good, stakes an acceptable middle ground between IV's railroaded plot and V's customizability but flakes in the World of Ruin for me. I is big jank but it's wholesome classic jank that I still replay annually.

V > VI > I > IV > II > III I guess