Part of my goals for this game is to create a more consistent difficulty curve, while still retaining variety in encounter types. This is something I can't do without your help! I can test my own battles as much as I want to, however I'm not a blind runner and can't replicate how another player who thinks differently from myself will approach a battle. There are some battles that still seem out of place in my opinion, but I'm also not sure if anyone else finds them troublesome or not.
Anyone who has played through a good portion of the game can write their own rankings. Use whatever scale you want, but please explain it if it's not the same one I'm using. Keep in mind some of the differences within versions - if a battle has changed drastically since you last played it, please note that. All of my rankings are based on battles in the newest version (2.55 as of this post)
All newly added battles that didn't exist in vanilla are now in italics. 
No longer relevant notes removed.
Note: Rankings in story battles are based off of not using sidequest equipment or characters. They assume a "normal" party (Ramza, Agrias, and whatever monsters are available at that point in the game; with reasonable stats/equipment/jobs and abilities available). They do not assume excessive amounts of grinding (i.e, Bard in ch 1) or unreasonable recruitment (all 74/74 units).
Chapter 4 end sequence and chapter 5 ranking assumes lv 99 party (since reaching it at low levels in current versions is an unreasonable assumption). Extra battles ranking assumes a ch 4 party (but you are free to attempt those as soon as it opens for you for the extra challenge).
Scale: between 0-10, where 0 is "must actively try to lose" and 10 is "evil" Note that the battles are ranked as compared with each other - it's not necessarily an even difference between a 1 and 2 vs. a 7 and 8.
Added: Current average to each chapter, battle count.
Chapter 1:
Orbonne Intro - 1
Gariland - 1
Mandalia - 1.5
Igros Castle - 1
Sweegy - 2
Dorter 1 - 2.5
Sand Rats - 2.5
Miluda 1 - 1
Mandalia 2 - 3
Miluda 2 - 2.7
Wiegraf 1 - 2
Algus - 2.8
Current battles: 12
Ch 1 average: 2.1
Chapter 2:
Dorter 2 - 2.5
Araguay - 2
Zirekile - 3.5
Zaland - 5.1
Zaland 2 - 4
Barius Hill - 4.5
Lionel Gate 1 - 4
Zigolis - 4.8
Goug 1 - 5.1
Goug 2 - 4
Warjilis Port - 4.8
Barius Valley - 4.5
Golgorand - 5.4
Gafgarion - 5.5
Queklain - 5
Current battles: 15
Ch 2 average: 4.3
Chapter 3:
Goland - 5
Zalmo - 7
Outside Orbonne - 5
Book Storage 1 - 6.5
Izlude - 7
Wiegraf 2 - 5
Dorter 3 - 5.7
Lesalia 2 - 6
Grog Hill - 6.5
Yardow - 6.4
Yuguo - 5
Riovanes Gate - 6.5
Velius - 8
Riovanes 3 - 7
Rooftop - 4
Current battles: 15
Ch 3 average: 5.9
Chapter 4:
Doguola - 8
Meliadoul - 7
Finath - 9.5
Zeltennia 1 (Ruins) - 7.5
Zeltennia 2 (Castle) - 8
Zeltennia 3 (Church) - 7
Zalmo 2 - 8.5
Balk 1 - 9.1
South Wall - 9.6
North Wall - 6.5
Sluice - 8
Bethla 4 (Final boss?) - 7.9
Zarghidas Slums - 7.5
Zarghidas 2 (Juiblex) - 8.1
Germinas - 7
Germinas 2 (Duma) - 8
Poeskas - 9.3
Limberry Gate - 7
Limberry Office - 8.5
Elmdor - 8
Zalera - 8.5
Igros Gate - 8
Adramelk - 9.2
Balbanes' Grave - 8
Murond Gate - 7.5
Murond Hall - 6.5
Zalbag - 9.1
Orbonne Chapel - 8.5
Book Storage 4 - 7
Rofel - 9
Death City Entrance - 9.1
Kletian - 9.2
Balk 2 - 9.7
Hashmalum - 9.4
Altima 1 - 8
Altima 2 - 8.9
Current battles: 35 (36 if you count both Altimas separately)
Ch 4 average: 8.2
Chapter 5 (work in progress):
Zeltennia 5 - 8
Fort Zeakden 2 - 7
Fovoham Windmill - 9.2
Fovoham 2 - 9.3
Riovanes Gate 2 - 9.8
Bervenia Volcano - 9.4
Inside the Volcano - 9.5
Zeklaus Desert - 9.5
Dorter 4 - 9.6
Sweegy 2 - 9
Gariland 2 - 9.6
Inside Military Academy - 9.7
Outside Murond - 9.7
Inside Murond - 9.8
Murond Chapel - 9.5
Goug - 9.1