General

Thanks guys, next time i'll include some important details to put into consideration (e.g. my range; clean and buffed)

I'm just going to go off of normal since you probably would have stated hard/chaos if you wanted those.

10 - Zak (Not an issue anymore)
9 - Hilla (Quite a fun battle but the unlimited number of deaths makes it really simple, only reason not a 10 is due to her resistances)
4 - Ark (Not that difficult of a fight minus the full screen unavoidable insta)

Root abyss
6 - Queen (Zone your character correctly to avoid the swipes and just tele behind her for her breathe, she does have a DR face but I've never had to see it)
10 - Pierre (Just don't attack on opposite hat)
8 - Von Bon (Hits hard but just keep your hp up, use your class movement skills and jump when he slams the ground)
7 - Vellum (There's no tail to avoid and he faces the direction he's moving while underground, just stay behind him and hit him)

6 - HT (If you can't kill arms quick enough or you don't have backup plans/status resists, seduce chains can be an ender)
4 - PB (~10bil hp, not so much a DPS requirement rather than being focused and avoiding attacking during DR)
4 - Von Leon (if you don't kill his minions fast enough he will regen hp, also he does have DR)
1 - Magnus (keeping in mind normal and not easy, attack and defend not all of either)

Not sure about the easier versions since I don't do them but for the hardest ones in terms of time/effort it takes soloing it goes:

10-Czak
10-CHT
9-Normal Ark (Just because of the 1hit)
8-Hell Gollux (Lower if you don't have enough DPS, once you do it's a 10 though)
7-Hard Hilla (Lower than 7 if you have trouble killing her even with binds)
6-CQueen (Not too hard but lots of HP)
5-CPB (Tons of HP+DR not really hard but takes a while and you only get 1 life soo)
4-Hard Magnus (Same as with Hard Hilla, depends on DPS, the fact you have 30 lives makes it fairly easy though if you can dish out the damage and use binds/equilibrium correctly.)
3-CPierre (Can't really use reflection and spectral is kinda weaker+has a longer delay and is less maneuverable. Just sort of a pain for most people to finish him off as well.)
2-CVon Bon (Our skill delay makes it hard to keep steady dps when you have to watch for ground pounds/I always die here a lot)
1-CVel (Takes a huge amount of dps and practice to solo, skill-wise the hardest boss in the game imo)

Your range is kinda of important in determining order too since the ones you can bind will get easier and easier the more hp you can take off before they can move.
A lot of these I'd probably give lower numbers if I was weaker, like Hilla, Ark, Magnus

i feel like normal magnus is so much easier than hard hilla..

@GoXDS: the relativity is flaws here, I mean, if easy zakum is 10 and hard magnus is a 1, then all of the 2~5 should be something between 1.2~2.
But then again, it's just a simple question, and an answer for the TS.

[quote=natty2]Some of them have different diffuculty levels.
I'll note those too.

This is opinion based purely, and if anybody dissagrees, well, then I don't care xD

Easy zakum - 10
Normal Zakum - 10
Easy Von Leon - 9
Easy Horntail - 9
Normal Hilla - 9
Chaos Zakum - 9
Normal Horntail - 8
Normal Von Leon - 8
Easy Arkarium - 8
Normal Pink Bean - 7
Chaos Horntail - 7
Easy Magnus - 6
Normal Arkarium - 5
Root Abyss (Normal) - 5
Normal Magnus - 4
Hard Hilla - 3
Chaos Pink Bean - 2
Root Abyss (Chaos) - 1
Hard Magnus - 1[/quote]

not sure if it's because you're overstating/understating some bosses but uh
Easy Magnus was nerfed to the ground. should be much easier 6->8
RA should definitely be extremely easy, especially compared to PB or CHT who both have DR and no respawn 5->8
CZak still has Seduce and no respawn and pot-seal so should be harder, at least not easier than HT 9->8
well, I don't like the numbers I assigned either but I have to disagree with some of your relative difficulties

Some of them have different diffuculty levels.
I'll note those too.

This is opinion based purely, and if anybody dissagrees, well, then I don't care xD

Easy zakum - 10
Normal Zakum - 10
Easy Von Leon - 9
Easy Horntail - 9
Normal Hilla - 9
Chaos Zakum - 9
Normal Horntail - 8
Normal Von Leon - 8
Easy Arkarium - 8
Normal Pink Bean - 7
Chaos Horntail - 7
Easy Magnus - 6
Normal Arkarium - 5
Root Abyss (Normal) - 5
Normal Magnus - 4
Hard Hilla - 3
Chaos Pink Bean - 2
Root Abyss (Chaos) - 1
Hard Magnus - 1

Zak, Hilla, HT, Root Abyss (norms) are all pretty easy and straightforward.
Arkarium is easy too, just his Undodgeable Instakill spam ended many a runs for me.
Never done Pink Bean, or Von Leon.
Magnus is just crazy.