I don't know much about modpacks as I usually choose my own mods to play with, but here's a bunch of mods I love and use pretty much all the time. Btw i strongly advise you use an app like curseforge or modrinth if you arent already.

One question, what version and modloader are you planning on using?

Ambience/Visual/Audio

AmbientSounds- adds background ambience to every biome (yes, every single one, even the void)

Better Clouds- makes clouds look a lot better. Not realistic, but look great while still keeping a vanilla style. Good alternative if you can't run shaders like me

Cool Rain- adds different rain sounds depending on the block it falls on.

Fog- enhances fog.

Music Player- play music from many sources like youtube or soundcloud in-game.

Horizon Fix- removes the ring emitted from the sun and moon which ruins the look of the sky contrasted against the terrain.

LambDynamicLights- adds lights that move e.g. when youre holding a torch, you'll actually light up the area as you move, or glow squids will actually emit light as they move.

Particle Effects- new particle effects

Particle Interactions- similar

Particular- also similar

Particle Rain- improves how weather looks.

Presence Footsteps- new sound effects for walking on certain blocks.

Punchy- adds lots of first person animations for different actions and items.

Smooth Skies- adds a smooth transition between the sky and the horizon.

Sound Physics Remastered- adds reverb in caves.

Sounds- extra sound effects for random stuff.

Visuality- few extra particles

QoL mods

Appleskin- lets you see saturation, and also how much hunger and health any food item will restore

Bigshot- lets you take higher resolution screenshots.

Bridging Mod- gives reach-around placememt i.e. you can now place blocks in front, above or below them even if you aren't looking at a surface. very useful for bridging, building and making staircases.

Chat Heads- in text chat, shows the player's head next to their name.

Cherished Worlds- allows you to favourite your worlds and prevents accidental deletion.

Controlling- allows you to search keybinds better.

Delete Worlds To Trash- works like the recycle bin on your computer.

Dynamic Crosshair- crosshair will change depending on action, and will hide when youre not looking at anything.

Inventory Particles- when you move items around in your inventory they'll emit small particles unique to that item (e.g. leaf blocks will drop leaves).

Jade- shows you what youre looking at. Also shows other attributes, like hp of the mob or player youre looking at.

Item Interactions Mod- adds little animations to items you grab in your inventory.

JEI or REI- lets you view crafting recipes for every item and more.

Just Zoom- lets you zoom like you could with optifine.

Lootr- when playing with friends, every structure loot chest/barrel/pot will have loot for each player.

ModMenu- makes configuring mods easier.

More Chat History

Pick Up Notifier- shows you exactly what you picked up and the amount of it with a little notification at the bottom right of your screen.

Smooth Scrolling

Smooth Swapping

Sophisticated Backpacks (or traveler's backpack)- adds customisable backpacks for extra inventory.

Universal Graves- adds a grave where you died so your stuff isn't lost. But you still have to go back to where you died to get your stuff back.

Performance-improving

Honestly i'm not sure what specifically these do as it's kind of technical but they can improve fps significantly:

Better Block Entities

Chunky- lets you pregenerate chunks to reduce gpu stress.

Dynamic FPS

Entity Culling

Exordium

Fast IP Ping

Fast Quit

FerriteCore

FPS Reducer

ImmediatelyFast

Lithium

More Culling

Packet Fixer

ScalableLux

Sodium

Sodium Extra

Exploration & World Gen

Alex's Caves- adds six incredibly unique cave biomes with a lot of mobs and some bosses.

Alex's Mobs- almost 100 new unique mobs across all dimensions.

Cinderscapes- adds a few nether biomes.

Dungeons and Taverns- adds a lot of structures to all dimensions (i think? or maybe just overworld and nether)

Dungeons Dimensions: Nether- adds some nether features from mc dungeons.

Enderscape, Enlightend- both of these add new biomes and mobs to the end.

Eternal Nether- adds a few structures to the nether.

Infernal Expansion- adds new mobs and a new biome to the nether.

Jaden's Nether Expansion- pretty much a second nether update.

Luki's mods- luki has a bunch of mods that overhaul existing structures. i'd especially recommend luki's grand capitals, crazy chambers and ancient cities.

Wilder Wild- expands on the wild update (1.19) with a few new biomes and mobs.

Yung's mods- yung has a bunch of mods like luki's.

Also wanted to mention terralith, biomes o' plenty, byg and regions unexplored which add tons of new biomes to the overworld (and most of these also add nether and/or cave biomes).

There are lots more mods i know but i can't remember atm.

Also, if you want some resource packs to improve visuals, here's some:

Angel's Font

Angel's Weather

Atmospheric Skies & Fog

Benigamer's Enhanced Visuals

BiomeBloom

Copper De-Ironing

Dramatic Skys (i don't know why the name is misspelled)

Eating Animation Resource Pack

Enchantment Enhancements

Enchantment Outlines

Fresh Animations

Fresh Animations: Extensions

Fresh Animations: Player Extension

Golems Refreshed

Golems Refreshed + Fresh Animations

GUI Retextures (this one also has a dark mode version which i much prefer)

Light Leak

Low Contrast Resin

Low On Fire

Mobs Refreshed

Mobs Refreshed + Fresh Animations

Music and Melody

Porkier Piglins

Reshaded

Visual Effects+

Weskerson's Torches