Using 28 planetary space what is the best attack, defense, and cloak mixture option to render a planet most resistant to being conquered and invaded?
(This is assuming the player has maxed out the research on planetary attack, defense, and cloak structures.)

keep in mind, even if cloak is maxed there is still a decent chance a higher level could scan it.
i prefer a tad bit of cloak (special structure if possible)
Mostly defence and a bit of attack (usually a 3:1 ratio)

I don't mix defense and attack myself, mainly because then they can use two effective debuffs on my planet instead of one. I usually go all defense because the debuff for defense is less effective than the debuff on attack. I don't bother with cloak because if I used the same amount of space needed to put a decent cloak on a planet then my planet is still effectively protected from weaker players and it has better odds of not being invaded by a higher rank player who would probably find it anyway.

if youre guarding an amazing planet, a little cloak goes a long way. go with the 14k defense and 800 cloak. that should keep it relatively safe. it will still get found, but its less likely to get found by scan multis or low level legions.

Got to agree with red, defense is much better to have then attack due to artifacts. Though i do recommend some attack nit much though, just enough that combined with some population the attacker will most likely have to repair. Giving you some time to cap the population and guard it.

If ye try te defend a planet and the planet is good enough, regardless of what ye put on it it can be taken from ye. This is how mission worlds get stolen, probably with alarmin frequency. Best defense fer a world is te no get scanned, an if ye had the 3.2k cloak, an arr in a legion worth a spit, ye arr looking at 6.4k cloak not includin passive bonuses an not includin if yer legion's o'er 50 members. Get it te 60, an ye have 7,040 cloak jus from structures, easily close enough that, if the worlds really worth all that te ye, ye kin get yer cloak o'er 10k wit some passives added er other stuff. While 10k cloak's not impervious, tis gonna be darn hard fer all but a couple dozen players in te game te find.

While I use one o te best cloaks fer my lower end worlds an add some defense an attack, tis because worlds are made ferr making stufff, not jus sittin behind giant barriers o shileds and masses o minefields. Cloakin up jus a lil tis far better than having anyone wit a scanner able te see yer planet, an then them getting the right people te take it off yer hands. Many an unscrupulous multi-acccounter has been spotted wit a rank 20-30 ship they keep scannin wit an resetting. If ye arr not cloaked at least a lil, then those small fry'll be selling yer goods te someone capable o takin 'em within a day er so o finding 'em. Less arr the odds of a player big enough scanning a world than a player who scanned selling it te a legion fer some easy credits er artifacts.

Only catch te cloak is ye got te still be playin te keep yer worlds cloaked. Pirates stole a mission Dyson some 2 weeks ago because the owner went inactive an it's cloak counted fer naught. As was common fer inactives, they were driftin legionless, so no bonuses fer thar worlds. The 11k defense an 10k attack didn't stop even te first assaulter from gettin it. (Well, an a merciful RNG...)

I used to prefer Attack, but the evidence is stacking up against it; I'm thinking of switching to only one Quasi-Chaos Minefield (or preferably two Lazuli Darkmines) on my planets, and the rest defense.

Is cloak really worth the space, I mean any high level can scan it , and even if a low level scanned it, they couldnt take it if it had the def.attk structures,,

some higher levels use multi accounts to scan planets for them since they hit the end of the scan branch in the research tree. so you do have to worry about that. and i mean in general, not naming any specific names or legions. but whenever you see a legion with 4 or 5 inergon explorers that are around rank 20-40 that never seem to level, you can bet those are multi accounts.

3200 cloak on my 15x, more and it ends up wasting resources. Blocks the majority of players. No sense losing 20% more production across the board for double cloak most of the time. Mining planets I don't even bother with cloak or def anymore, they can be replaced easily and I'm at my limit for mining anyway (RP is the new mining lol). Now for ppl not using cloak, attack has got to be the strongest now with the darkmines. Even with the debuff stronger on attack, you will get about 25% more total defenses out of it than defense structures. Honestly tho, you can blow 30k defenses to hell if you have enough sabs, I don't trust it anymore; that's why I am doing cloak. Note with the new max scan raised, you need 10-12k cloak now on your storage worlds or others you can't afford to lose.

I am really surprised only Ix and I chose cloak, and furthermore no one chose pure attack as a tactic with darkmines out there. The math speaks for itself.

I thought Artifacts were the new mining. lol

The problem is, invasion calculations only count 60% of the Attack, so with 2 Darkmines on a planet, Attack is still less than defense in terms of invading.