Currently I am noticing that when you move heroes around in a group, the game will automatically assign a level 1 4* troop to them even when a much better 3* troop (say, lvl 15) is available. I don’t know if this is a recent change, or is only showing up and noticeable now that I have a couple extra 4*s of some colors.
Game should pick the troop that will result in the highest TP score.
It picks the first highest leveled troop available to that hero based on points and then works down the line from there.
So if you want a different one then you have to change it manually.
Then it’s currently calculating the ‘points’ incorrectly. A lvl 1 4* is in no way better than a lvl 15 3*, and the latter results in a good bump in TP score when switched to.
That’s actually hard to say as we can see the individual points allocated to a troop other than once it’s added to a hero and the could be different with each hero.
Maybe this might actually be a good question for a new request to be able to see a troops points or even ask @zephyr1 and others how troop points are actually calculated.
Until then I guess it’s all guess work.
I just pick troops based on whether I feel that hero needs more attack or shielding etc. What I have found is a 5* hero will take a 4* troop before a 3* troop and maybe that plays a part in it as well.
Here I found this which may help solve the question.
It does within a given rarity.
I think this might be your issue, depending on how you’re doing it.
As you set heroes, it defaults to the highest Rarity and then TP Troop for each.
But if you have multiple heroes of the same element, when you remove one, the Troops on the others stay unchanged.
To imagine a scenario, say you had 2 purple and 3 other heroes, and then you:
Removed a non-purple hero
Added a third purple hero in its place
Removed a different purple, dropping back to 2 on the team
Then you’d end up with a lower power Troop on the new purple, because the higher power Troop would have been held by the purple that wasn’t removed until after the new one was added.
Here are screenshots of that in action:
The game agrees on the ranking of those Troops in terms of power, although I don’t know if I’d say it’s a “good bump” — a Level 1 4* is worth 41 TP, and a Level 15 3* is worth 45 points.
So it’s a 4 point bump.
This formula appears correct, and the resulting observation is useful:
Based on that, a Level 11 3* and Level 1 4* are equal for points — so the Level 1 4* will be chosen first by default unless you have a Level 12 or higher 3*.
But it does appear that Rarity trumps Power in selection of a default Troop.
I started using Kerridoc 's team idea of putting my current leveling projects as Team 1 and Team 2.
Then I noticed the 1* Troops from Team 2 kept being assigned when I created new teams.
Then that stopped happening.
So recent?
Also why does it pick my least used battle items if I buy a new team slot?
Currently it appears based on the number of stars. 4* before 3*. ( edited )
Then on team power ( edited )
If a tie, it then picks oldest troop by summons date.
It doesn’t it goes on rarity first and tp as a decider afterwards
I just tested more, and I think you’re right.
It had seemed initially to me in testing that it was using TP, but I just futzed around more in Beta with Troops at several different levels and it appears to prioritize rarity first by default.
I’ll edit accordingly.
This change has been made with V27 but was not in the release notes list. I have high 3* troops that are now auto-selected before 4* troops when setting up titans teams. This can probably be closed once verified.
Seems to work for me too, I ended up with these Troops selecting heroes from left to right, starting from an empty team:
Bump, please close out as this has been implemented.
Closing as implemented 
