Which 6 Pokemons?

Usually I find both, the order and the selection suggested, asinine.

i use:
vaporeon 2585 Wgun/aquTail
gyrados 2459 bite/hydroP
Dragonite 2448 dragon/hyperB
dragonite 2230 dragon/DraClw
lapras 2177 frostB/blizard
charizar 2076 wing/flamtow

no tower resit me, i can kill 10pokemon 2K5+ easy ;-)

I think, but don't actually know for sure, that the game suggests most (if not all) of the six pokemon based on two things: 1. The first defending pokemon's type, and 2. Your highest CP pokemon. For instance, if the first defender is a Vaporeon, the AI will usually recommend my Exeggutor, Vileplume, Dragonite, and some other stuff in that order.

Sometimes though IDK WTF the game is thinking - every now and then when I go to take down a level 10 gym it will load my lineup with five 1500 CP Jolteons while leaving out my 2600 CP Dragonite and 2400 CP Vaporeons... It's like, nah brah, Team Jolteon will get me nowhere in a hurry.

It seems to give a suggestion by type.. like if there's 2 exeggutors and a dragonite it gave me 5 flareons and a dragonite. My flareons are weak and I have a lapras. So it's not great suggestions, just kinda like "eh, these should work..."

I don't trust in the system suggested pokemons, it usualy gets wrong, especially considering dual types pokemons. I always carry a special selected group of my six best pokemons to every battle

I do not trust in the suggestions... they're actually very mistaken sometimes, most of times I look at the defending pokemons and choose my own team, that eventually presents a better final result in the battle

My experience has been that the 6 pokemon are listed best to worst at their ability to beat the TOP pokemon in the gym.

Which is utter nonsense in any non-trivial gym, as merely getting to the top pokemon can be hard (and the last thing you want to do is use your best counter to the boss right off the start...).

Its weird cuz a few months back it seemed like the recommended lineup was close to the ideal lineup. Seems like during the last couple updates that was changed. But yeah manually adjust my atk team on gyms.