Best levels for coop?

Looking to make a character to go through the game multiple times (NGs) and do a lot of cooping. What would be a good level? I'll star the levels I enjoy playing.

Worlds are:
Undead Burg ***
Undead Parish ***
Lower Undead Burg ***
Depths ***
Blighttown ***
Sen's Fortress ***
Anor Londo ***
Painted World of Ariamis ***
Darkroot Garden ***
Darkroot Basin ***
New Londo Ruins
The Duke's Archives
Crystal Cave
Demon Ruins
Lost Izalith
The Catacombs ***
Tomb of Giants ***
Kiln of the first flame ***

I like playing all these starred levels, some more than others. What would be a good level to play most of them? I'm thinking 30 or so.

Undead Burg 5-12
Undead Parish 10-19
Lower Undead Burg 16-25
Depths 20-30
Blighttown 25-35
Sen's Fortress 35-45
Anor Londo 38-50
Painted World of Ariamis 42-55
Darkroot Garden 20-35
Darkroot Basin/Forest 35-55 (it really variates, most people go here after beating Anor Londo)
New Londo Ruins 42-60
The Duke's Archives 45-60
Crystal Cave 48-60
Demon Ruins 45-60
Lost Izalith 50-65
The Catacombs 25-45 (it really variates when people choose to go here)
Tomb of Giants 50-65
Kiln of the First Flame 50-75

You forgot these:
Royal Woods (with Artorias) 45-55
Royal Woods (with Kalameet) 50-60
Oolacile Township 50-60
Chasm of the Abyss 55-70

Best places (most traffic) are Anor Londo at level 42 or any DLC area at level 52-55. NG+ you can go with Anor Londo 85-100 and any DLC area at 85-100.

You're not far from 42, so I suggest you go for that level and stay in Anor Londo. You can help also with Sif, and Four Kings with good results at that level too.

At 30 I could hit lvls 17 - 43 right?

So that would be a large portion of the levels. Didn't include DLC because I haven't bought it, not sure if I will.

At 42 I could be summoned by a host levels 27.8 to 56.2 (28 to 56?).

I'd like to note that my level 50 toon gets tons of traffic in Sen's fortress (invading and summoning).