The main issue i see here is that at different rank ranges your perceptions change for example high rank players who's colanize costs are 20b+ wont take many "good planets" because the cost is to great but i'll give my thoughts as a mid/high rank player

My method when taking planets is to maximize arti and have as few non arti planets as possible.

Research
Bad- anything below VM gas ea
Medium - VM gas rich
Good - vm and C plasma's at least mega rich
Great - C plasma's 15x+

Mineral

Really you don't want to be taking anything that's not a VL toxic or a maxed demon along those lines

But for lower rank players i'd say VL ER volcanics can be ok but they'll be dead weight when you start building max toxics.


Arti

Bad - anything below VL VR
Medium- small 1x VL VR VL ER
Good S 3x average 1x large mega Massive ultra VM ER
Great- anything above VL 3x


This is roughly what i go on when taking planets with an colonize of 4b and an invade of 8b the standards will keep going up as my costs do though.

ARTI PLANET advice
Dont steal/invade any planets that are smaller then massive from someone in a decent legion (check with the search legion button from the legion page) if they're a free floater then its your choice to decide if they can steal it back alone.
the reason for this is because youll need to put defences on it.
use DARK artis, they add cloak as well (incase you ever flux it) and OBVIS, if you dont have obviation barriers, GET THEM NOW, its the cheapest research tree to get to the end, and you only need 1/3 to build them.
if your taking anything smaller then massive and mega rich, (from unoccupied/unscanned) put 1-3 defences on it (two obvis and a dark one) and it should be safe from the majority of people. I would recommend taking nothing smaller then LARGE though and i only put one def if any on them. since their fairly easy to replace.
my only exceptions are exotics and they need to be atleast x5 in TWO areas, arti being one of them, and just max out production on them you can fit two +12s and 3 single space artis on them. my x6 is pumping out 277 arti/hr. which is as much as, or more, then a massive extr rich with def on it..
The difference is, with the talth ability, the massive and bigger planets quickly outshine the smaller ones because they grow their production much higher because of the extra space.
for VL planets, i throw on 3 +12s and 3 single space artis. anything over MRx3 gets 3 obvis on it atleast and maybe some cloak. (yeah im not always consistent)
anything thats massive or VM, gets ~10-15K def, ~1-2K cloak and then just production.

MINING PLANETS.
ONLY TAKE TOXICS THAT ARE VERY LARGE, you can try to only get the 'correct' even numbered richness so it goes to x18 when you make it irradiated, but honestly the difference is negligible. my massive x 18 with 8774 def (after legion bonus) is pumping out 693 an hour. and my x17 massive with 9416 def, is pumping out 685.85 an hour... so its your choice, do you care that much for 7pts of production.. i certainly dont. I throw on ~10K def and the rest is production.

Research planets... well not my best area, ive got a bunch, zero defences on ALL of them except my one paid for x17 colossal plasma and its got 10K def.
(at rank 645 now, and sold the x15, still have the x17 for now)

as for storage planets. people have different view on this. 99% say go for max cloak, well thats all fine and dandy if you npc like mad, and have the dark badges to get the magnetospheres for them.. i personally DONT, so i go for defences and ~10-12K cloak, which will keep most people from ever finding them.
and honestly, if someone spends the cash to be able to find them (they need to be an explorer and use limited artis) then theres a damn good chance that they can take them no matter what the defences are. but saying that, i slap about 60K on them. pretty much every space that isnt storage or cloak, is defence.


anyone care to add anything or personal preferences then please add whatever you like.