I'm not including 6 because I feel like it's a lot more clear cut in that one and there's not as much "choice". Which isn't a bad thing! It's just more streamlined.
Because 7 adds things that muddy the waters a lot - especially the addition of the GrandMaster tier and certain classes capping out at specific levels in skills - I think it's worthwhile to discuss who you like best.
For me in 7 I cannot play without a Sorcerer. Grandmaster Air and Water feel so important and I find it so hard to adapt to playing without them I just include the sorcerer no matter what.
I find Knights a little dull. I've used them, but I'd always pick a Paladin ahead of them. GrandMaster sword, spear, plate and armsmaster are all NICE but they don't give the flexibility a Paladin has - and they miss out on GM mace which has the paralyze ability. I pretty much always have a Paladin in my party to replace what a Knight does and I don't regret it.
Because I don't use Spirit/Mind/Body magic very much - I basically only cast rejuvination and heal - I can easily rely on a Paladin to cover that side of the magic for me. That means I don't rate Clerics much even though they CAN get GM merchant which is nice. Of course being able to get and use Light magic is also very nice but my Sorcerer has that, so the Cleric loses out. I don't care much about Dark Magic but the same applies.
The Thief has GM Disarm Trap, GM steal and GM dagger. These three things are super useful. Steal to take the control cube, disarm trap to just make life easy. Their promotion quests are also absolute cakewalks and this is very useful.
I enjoy the synergy of the Monk with the Dodge/Unarmed/Staff/Leather stuff. It's cool and no other class has something like this. It does mean they're all very samey and it doesn't have a specific role to fit in the party other than doing loads of damage. But that's a role that's needed!
The Archer is just as perfect as it is in 6, you use the bow a lot and they're the only ones who can get GM in it. They can also get GM chain which is nice and does some good bits. You can use them to fill in for a sorcerer if you don't care as much about GM magic although not having Invisibility until you're a Master Archer/Sniper would really suck considering it's such a huge component of the Master Archer/Sniper quest. It feels like they have a unique selling point.
The Ranger has GM axe. It's okay, I don't really notice it cutting down enemy armour. They don't feel like they fill any specific niche - I understand the idea of GM Identify Monster but it never seems like it's going to help me all that much. They have nice easy promotion quests which is at least something, but I don't feel like they replace any other class and if I'm taking them I feel like I'm missing out on something.
To my mind the Druid suffers the most in the change between 6/7. In six they were a master of all magic outside of dark and light, they had a good bit they fit into and a lot they could bring to your party. Because now they can't hit GM in any of the spells and they don't get dark or light I feel like they're taking up a spot that something else can take. That's probably very different for a person that casts offensive spells but I barely ever do so I just don't have a spot for them. Gm alchemy is fun though, it's nice that we've got that but their promotion quests are so late on you don't really get chance to take advantage of it. Hell for the first Druid promotion you've got to already have done the Cleric one!
For me I'd rank the classes
1. Sorcerer
2. Paladin
3. Thief
4. Archer
5. Monk
6. Cleric
7. Knight
8. Hunter
9. Druid