My casting classes (besides Paladin and Shadowknight. Ranger should not use spells):
Sorcerer: CON + CHA as top two stats. Spells require no verbal component or materials, as they are innate casters who perform magic simply by feeling and gesturing to where they want their magic to take place. A focus item can still help them control their power. Spell school specialization will involve 7 bonus tiers (for every school you choose to not be able to know, you gain a tier in another school) and you can choose to specialize in multiple schools. Wild magic option won't involve specialization or even choosing any spells to know; instead the Sorcerer can try to do anything that could be cast at their level, but the results will vary. Spellcasting limited when wearing armor.
Wizard: INT + WIS as top two stats. Each individual spellslot must be specifically prepared, but any individual slot can be changed with some minutes of spellbook study. Spells require verbal and physical involvement, and focus item (unless prepared/learned to not require it). School specialization will be more complex than Sorcerers; instead of choosing which schools your character will never know at Level 1, you instead choose what to study at every level. Can perform rituals, materials are required for most. Spellcasting limited when wearing armor.
Psionicist: INT + CHA as top two stats. "Spells" only require thought (but physical involvement can help to manifest it) and spell slots are not used, everything is determined by mental power points. Their 3 spell schools are Telekinesis, Telepathy, and Mind Control. At every level you choose 1 school to rank up (only 1 school known at Level 1, each school has 20 ranks). Spellcasting limited when wearing armor.
Cleric: CHA + WIS as top two stats. Casting will differ per spell on what is required (verbal, physical, focus item). Can perform rituals. A very limited amount of spells can be prepared per day, although they can always choose on-the-fly to cast a "generic" spell from their favored school (Healing, Protection, Divinity, Smiting). A handful of spells will be deity-specific, but otherwise all spells will be known.
Druid: WIS + DEX as top two stats. Spellcasting similar to Sorcerers, but sometimes need to have the right components or conditions for full power (having seeds to magically grow into the kind of plants you want to use, having animals nearby to gain power from, having access to the sky for storm magic) and they learn spells through the experience of interacting with a biome, rather than only knowing a limited selection of spells. Their 4 schools are Plant, Animal, Storm, Nature (healing capability found here). Spellcasting limited with more than leather armor.
Shaman: WIS + CON as top two stats. The majority of their spells will require material components to work and the majority of their spells will take longer to cast than what is typical for other casters (I don't mean rituals, but they will be able to do those and also make potions). Their schools are Curses, Cures, Channeling, Communing. In their one favored school they will eventually be able to learn all the spells by communicating with spirits, in the other schools they will just know a handful each. Can cast a large number of spells per day. Spellcasting limited with more than partial chain/scale armor.
Bard: CHA + DEX as top two stats. Instrument required to "cast" some of their "spells", and most will benefit with an instrument. No spellslots, they just choose which songs they want to prepare for the day (can swap a song with 10 minutes of prep) and can "cast" them almost constantly, with short duration effects unless they continue to perform the song. Performing a song for 2 minutes will increase its power and multiple songs can be combined into a full performance, with their effects being delayed until the end of the performance if the Bard wants. Each song will be tied to an instrument type (including voice), with one being specialized in. A handful of songs can only be learned via specialization, but otherwise a Bard can learn all other songs if they dedicate enough time to practicing their music or experiencing various cultures. Spellcasting limited with heavy armor.
Elementalist: DEX + CON as top two stats. No spellslots, everything will just be determined by "cool down" time for their abilities and which elements they choose to focus on (100% in one element, 75% in one + 25% in another, 50% in two elements, 50% in one and 25% in two others, 25% in all four). No verbal component required, but physical involvement is required for anything beyond basic element manipulation, and obviously being surrounded by more of a type of element helps them. Spellcasting limited by armor, depending on the element trying to be used.
These would all be 6 hitpoint classes and Sorc, Wiz, Psion, Cleric would only gain half benefit from CON stat or hitpoint increase feat - yes the Cleric! I see them mainly as priests, they don't train their bodies very much. When they are "battle clerics" it is because their God is empowering them to do so, not because their physical capability on its own is good. I would go back to 3rd edition attack bonus system, but with less total attacks at high levels (too much busywork), and modify the bonuses so that every class has ".25 / .5 / .75 / 1" bonus per level (only a whole number provides bonus). Sorc / Wiz / Psion are .25 attack bonus, Cleric / Druid / Shaman / Bard are .5, Elementalist is .75
Warlock is a stupid class that does not need to exist (it's already covered by Wizard / Sorcerer / Shaman; if you make a "deal with demon" that should be a specific gameplay situation) and has only ever been cheese in D&D. I'm not interested in Artificer existing either, but it shouldn't be a casting class if it does.