PS1
I never touched IX. The game has no appeal to me.
Best: FFVIII while a flawed game that has a hard to learn Junction System, if one is not used to RPGs and/or skips tutorials, this game was my introduction to FF. It took me years to master the Junction System, but once I did everything became a cake walk. I wasn't and still am not a big person for love themed games/stories, but I still manage to enjoy FFVIII's story. Triple Triad is the most addicting side game I have played across the entire FF mainline series. The GFs are cool to me, and I enjoyed all of the Limit Break spamming I got to do later on in the game. The 4 part final boss battle is still my favorite final boss from the games I have played.

Worst: FFVII Imo, FFVII isn't a bad game. However, this game while it does have a story I enjoy and some fun side games, the battle system is just okay to me. It doesn't make me want to go back and play it over and over again. The original English version of the game has some horrible translation issues. Even as a PS1 title, it hasn't aged that well when compared to VIII and IX.

PS2
I never touched XI. It has no appeal to me.
Best - X-2 imo is a much more light hearted game within the series. While I can't say that I enjoyed the story due to being confused by it for so many years, the battle system more than makes up for it. X-2's battle system is easily my favorite out of the FF titles for both the PS1 and PS2 era. The game had a strong focus on attacking as a group and chaining attacks off one another to gain maximum damage. Cat Nip in the original version made the Cloister Trails a lot easier to get through and significantly reduced the threat level from most foes since Gunner Mode's Trigger Happy took advantage of the accessory best. Sadly, Cat Nip has been nerfed for the remastered version, so the trails aren't going to be as easy for me anymore QQ.

Worst FFX: I did enjoy the OST and storyline of FFX. Auron imo is a total badass. Sadly, these things could not be big enough pros for me to forgive the god awful lip sync issues of the English version, and a battle system that I just didn't enjoy at all. I like battle systems that make me think on my toes, which I had no option to do in X at all. X imo, isn't a bad game, but it isn't one of my favs by a long shot either.

PS3
Tried XIV on the PS3 or PS4. Stopped playing after 4 or 5 hours. The game just bored me.
Best FFXIII: The linear structure of the game didn't bother me at all. I really enjoyed the story of the game a lot. Most of the cast had good character development imo, with Hope having the best turnout. I liked the amount of strategy that there was to the more difficult battles. I was constantly experimenting with different party setups because every character had their pros and cons in combat. I also appreciate that the levels were capped during the story line so that way most of the storyline bosses would be challenging for me. I took it as a right of passage. Visually, it's a beautiful game even still today. The combat aspect did have some issues though such as the AI not always doing the most optimal actions and the fact 2 Commandos couldn't focus on one target if multiple ones were on the field. Also, there would be some frame rate drops when magic would fly all over the field. This wasn't something that killed the experience for me, but it was noticeable.

Worst FFXIII-2: Cauis, your awesomeness was the only reason I even finished the game. I don't dislike Noel and Serah, but my interest in the characters was also mild at best. I am glad Serah developed in a way that she wasn't still relying on her older sister by the games end. Noel's story aspect was not bad imo. There are a few tracks I can not stand from the game (the metal Chocobo theme song, and that rap song that got used early in the game). I didn't care for the monster taming thing. It reminded me of Poke'Mon "Gotta Catch Them All". Lightning should have never been on the front cover nor a part of the demo if she was mainly going to be a background character in the game. With me playing the demo, I had the assumption that the game would switch back and forth between Serah and Claire. That didn't end up being the case. Also, putting all of the hardcore bosses behind a paywall? GG SE GG. XIII-2 has been my least favorite game that I have played, and it'll probably always have that spot. The cons far outweigh the pros for me with the title.

PS4
Best FFXV: THE ULTIMATE BROMANCE!!!!!!!! I love the battle system. Ms. Yoko killed it on the soundtrack. I love the "fantasy based on reality theme", and for the most part I think that got achieved. I love the banter, especially when the bros are trash talking each other. I wish the campaign bosses were more difficult, but I am not blaming the dev team given how Japan thought Episode Duscae was too hard with their feedback.... -,-'. I'm still early in the game, but this is hands down my favorite FF mainline game of all time. The 10 year wait was well worth it for me. The game currently does have a lot of technical side problems though. For example, there is some thing called "frame pacing" that effects almost all versions of the game. I'm going to be playing this game for awhile.....

Worst FFVII Remake Part 1: I am pretty sure I'll enjoy the remake more than the original, but I've already played the original game. It just isn't going to be a completely new story. It will be interesting seeing if Advent Children, Crisis Core, and/or Dirge of Cerberus get implemented into the remake at some point. I'm not saying it'll be a bad game, but I'll enjoy it less than FFXV.