I have noticed that there seems to be a trend: In any given AD&D based game, there tends to be some class that is better than others.

In Baldur's Gate 1, it's bow-using fighters, because walking speed is slow (so ranged attackers get plenty of chance to hit enemies before they engage in melee) and there are fancy arrows such as detonation arrows available.

In Baldur's Gate 2, it's mages, because of the abundance of scrolls and the existence of many powerful spells (including spells like Time Stop and (Chain) Contingency). Also, mages can tank rather well (Stoneskin) and can even function as healers at high levels (who needs Clerics?).

In Icewind Dale, it's clerics because there are a lot of undead and clerics don't need to find scrolls (which are scarce here).

In Dungeon Hack, it's clerics, because they learn spells to deal with most of the dungeon's dangers (including being able to create food and magical weapons), and they are guaranteed to learn all their spells. Plus, their fighting ability isn't that bad. The only disadvantage is not being able to identify items.

What classes are best in the other AD&D games in these collections?

D&D is basically the game that is the reason behind the Linear Warriors, Quadratic Wizards trope.

Depending on spell selection available, mages will generally be the most powerful class once they gain access to 5th or 6th level spells. This does depend on the amount and types of support they have, notably healing to avoid death and meatshields to avoid melee.

Clerics are a good second choice, if the support for mages is lacking they take over the role as most powerful. Good armor selection, decent weapons and a wide selection of support spells.

For the games with parties, you definitely want a decent amount of both divine and arcane magic. In the low level games, some warrior classes are essential to keep your casters alive. A single thief can be an invaluable asset in all of them. But for the games with 6th+ level magic you definitely want mages for combat.

I remember one game (Savage/Treasures iirc) where I had 3 dual class cleric/mage characters. The only troublesome enemies were the magic immune ones, and the fighters handled those with buff backup.

There is no best class here because you play with a party of 6 adventurers (not counting the NPCs that might join you). You will need at least one mage and one cleric, and it's good to have several fighters/paladins/rangers. A good party for the 1st game is 2 fighters, 2 clerics and 2 mages (all humans). There are suggestions in the Adventurer's Journal, but they are usually not good if you intend to transfer characters into sequels.

In EoB and Menzoberranzan you are more limited due to fewer playable characters, but the principle is the same, though you may need to multi-class some of them to get magic and prayers. So in EoB you will want to have 2 front line fighters and a mage and a cleric behind, for example.

In several of the gold box games it's always best to have a paladin as the leader of your party. Reason being is that having a paladin as your leader for some reason allows you to actually control the moves of npc party members instead of having them act on their own. Those extra party members become far more reliable when you can make sure they don't do something stupid.

It depends on what chracter levels we are talking about, and what enemies they are facing.
In the Drow Caves in Curse of the Azure Bonds a Fighter/Thief is the best character.
At the end of Pools of Darkness a dual classed Ranger/Mage is probably the best.
At the end of Dark Queen of Krynn probably an Elf Fighter/Mage.
In BG2 the most powerful is probably a dual Kensai/Mage, but that one is frightfully boring to play.

Actually, I'd argue that a high level Wild Mage is the most powerful in BG2 (non-EE). Use Chain Contingency to stack 3 Greater Chaos Shields, and as long as they are up, Nahal's Reckless Dweomer becomes a reliable spell. You can now use your first-level spells to cast anything (including Limited Wish for more spells) and have the benefit of Improved Alacrity for free. There is now nothing stopping you from casting spells forever until the enemy dies. Who needs AC and physical damage when you have infinite spells?

I'll only speak to the Gold Box series, where you have 6 characters, and party balance is key.

I'll disagree with PetrusOctavianus about Dark Queen of Krynn: due to the linearization of the experience curve at high levels, single-classed mages become very powerful, able to effectively ignore magic resistance on draconians.

His point is otherwise excellent.

Generally due to the vicissitudes of the engine (it usually arranges your characters in two rows of three or one row of four with three in the back if you have an NPC) your front three or four characters should be fighters or multiclass fighters. (you can make #4 a cleric). You always need at least one cleric (in some games, like Death Knights of Krynn, you need three or four), sometimes one thief, and it's nice to have two mages.

Generic party:
Paladin, Ranger, Fighter/Thief, Fighter/Mage, Cleric, Mage. This will deal well with Curse, Secret, Gateway, and Treasures. For Pool, convert Paladin to Fighter/Cleric and Ranger to Fighter. For Pools, replace the fighter/mage with a second Ranger you dual to Mage almost immediately.

The Krynn games are a little more complex in the tradeoffs because multiclass characters can have higher levels. You should always have a Knight and a Kender Cleric/Thief. For the first two you can multiclass heavily--I've seen four Fighter/Cleric/Mages recommended--but as you get to Dark Queen you might run into level issues. I'd hedge and go with Ranger/Cleric, Cleric/Mage, Fighter/Cleric/Mage, and Fighter/Mage, though if you want to do single-class mages you can go with two ranger/clerics and two mages (red and white).

I found in the first two pools of radiance and curse of azure bonds it was all about the clerics hold person .
Wish I had of remembered dual classing I only have one char make it to SOS a cleric currently level 11
starting a new balanced human party to get a head start on pools.

I own icewind dale and balders I think not really a fan so idk enjoyed the gold box a lot more. I don't know why mostly the dungeon birds eye view thing they did they changed it I liked the old game mechanics better .