Alchemy!
No, I do not want to run around looking at the ground to pick a bunch of plants and stuff.
Smithing is a close second. Not only gather, but grind on the forge.
Enchanting is at least somewhat organic with found loot. Easy to find amongst other needed items (no need to scrounge extensively) and can be leveled through actual non-stop gameplay with supplying soul trapped gems to staves and items!
Enchanting. Actually, I like all of them, but enchanting I like least.
Smithing is usually fitting to the characters I like to play and I love installing mods that provide custom things to smith. Also, I've smithed a little bit in real life, so the idea of it just suits me.
Alchemy... well, I'm a bit of a hoarder/klepto in the game, so Alchemy is just a natural extension of that and a useful justification.
Enchanting... it just feels less natural. I have to think about it and plan it out and I hate, for some strange reason, enchanting anything with less than the most powerful possible enchantments. I will often just not use it.
Alchemy by far is the worst. I loathe it. I hate it. When I see a build that relies on it, I cringe. I hate farming mats. I hate grinding the skill. I hate experimenting and losing mats, time, and skill points you would have gotten otherwise. And even if you learn a few powerful poison/potion recipes, you find you never have the ingredients you need unless you go "farm" the mats. I'm sorry, but I've done enough farming of herbalist mats in my life.
Alchemy is my favorite (Even without Grinding it levels so fast!) And every ingredient needed can be bought at any alchemy shop, and has some awesome benefits!
Enchanting - I'm pretty neutral on this one, but I like to level it by recharging my Soul-Trap weapon with every kill using Azura's Star, then I can go on a kill-spree and level a crafting skill at the same time!
Smithing - Hate! Absolutely Hate it! I've trained it most of the times, and then either sell Banish Daggers or Potions to get the money back (KOI) Or just Steal it (With Ice Form or not!) It's just so... slow to level, and boring, and useless, since I will find those itens late-game anyway, And MfD is everything I need to augment damage and make every weapon viable, not some boring-as-hell skill
You clearly don't know you can just buy most potions from the same shops you just mentioned and skip all the farming, experimenting, dealing with potions with negative side effects or poisons that help targets.
Unlike smithing, where there is NO guarantee that a weapons/armor vendor will have the armor you want, alchemy shops always stock up on generic healing pots, poisons, and basic buff potions. The same goes for enchanting. You can spend most of the game and never get the item you want with the enchant you desire on it. But alchemy...it is so much easier to just buy the potions as the quality of the potions level with you from the vendors.
If enchanting were like alchemy, then sometimes you'd get a weapon that would heal your enemies.
If enchanting were like alchemy, then sometimes your health regenerate enchant would suck stamina out of you, or drain your magicka.
If enchanting were like alchemy, then you'd have to mix different types of soul gems together with different enchants to get "hopefully" the enchant you want.
Alchemy is my least favorite. I don't hate it, but I find it hard to motivate myself to put the time into it to make it truly useful. And the "new potion" noise is really annoying. I usually end up with a ton of potions that I don't use. It just doesn't go well with my tendency to hoard.