you ask the impossable, there are just way too many to choose. from franchises forgotten to ones squandered at the milking machine. but if i was forced to choose just one it would be the saga series and i will explain why. from its beginings it was a rather unique series the early titles while "simple" from todays standards were pretty good in their hayday heck their still fun and even have ds remakes, you had a weapon system in play and a proficency system too on a gameboy game no less. there was also complex systems involving monster party members something not really done often even in these days, again on a gameboy. they even knew people would have problems with npcs blocking the way, the solution? jump over them. now moving on to the romancing saga series this was where the systems really started blossuming hp was just a buffer for your lp in this series an easy way to think of lp is like a lives system almost certain skills or attacks could even reduce it directly and it wasnt really easy to increase either... and once it ran out that charactor was gone for good. sparking was introduced here too, while frusterating was amitedly a neat system that sometimes turned the tide of battle with a new tech apearing seemingly outta nowhere... then unlimited saga came along and introduced growth panels into the mix amoung a few questionable additions, one good one was lp was easier to refil in the form of going back to town. all in all the series had one constent that a lot of game series either lost or just dont have from the start they experiment allowing ideas to be tested and potently be intrograted into new games if they did well enough and discarded if it diddnt work out it constently was changing.