I tend to like 4 the best as well ... especially on double loot weekends ...
No one hunts 2 or 3 because of the doors... they really take too much time to open...
5 is okay, but found there isn't enough mobs
Lastly 6 doesn't have cards, and bosses don't drop 50's that really can add up ... plus the mobs die a bit slower than the other levels ... I found 6 is actually worse on double loot weekends as you have to wade through twice as many corpses many of them holding illusion cards and augs
At least 6 doesn't have stones of descent. Here is the best way to deal with the trashy loots on 6:
1) Set an audio trigger on your looter character for "upgrade" and have him leave all channels to avoid it triggering from people selling charms. Another audio trigger for "lore" is also a good idea, in case for some reason you are trying to loot a charm you already have (perhaps mid pull or something)
2) Take a 10 slot bag, and put a 1 stack of the 10 credit token in every slot. This ensures you can have 10000 credits worth of inventory space at least. You can do this for multiple bags. Put the bag lower down in your inventory (like, slot 6-8). You can do similar with the illusion cards, and kind of destroy them as you go.
3) Make sure the first 2 containers are completely empty. This is where all your stupid augs will wind up, as well as charm upgrades should you loot one. This way, you can easily go through and destroy your augs every couple pulls. You can make an audio trigger for II if you want as that will trigger when you loot a worthless aug, but this is kinda unnecessary.
4) If you decide to use eqbc (kind of a grey area, but it's not automating gameplay such that you could be afk farming) you can make a macro on the guy you are feeding the charms that is:
/tar corpse
/lootall
Then, while you are pulling mobs, you can have a hotkey on your puller that is:
/bct [charname] //keypress #
Where [charname] is obviously your looter, and # is the hotkey number. Make sure your looter has /lootnodrop never so that it just cleans every single corpse. While you are pulling, you can be mashing the button to have your other guy loot the corpses, which greatly increases your efficiency, since you can pull and loot simultaneously.
Final note: Manually loot chaos/balrog so you don't accidentally loot the pages/weapons and have them junking up your inventory.