For me it’s Soleal’s. I think that thing’s killed me more times than any other in the game (okay, I don’t get into Ultimate so don’t face celestials, Nemesis, etc). Always a bit apprehensive when I go in to tackle it. Only time I’m pretty sure I probably won’t die is when playing a petmancer. 
Which one’s the worst of the 3 for you? Or is the Sentinel the worst? I don’t really have trouble with that one very often.
was probably solael too
it has the most varied/significant direct attacks of them i think, not paying attention to purple flames can get you killed real fast, specially if you didn’t max resist by then
a bit easier to avoid eyes/deal with eyes on dreeg, and i’m legit not even sure what bysmiel guardian even does since never noticed anything “special” there 
Rashalga! 
Welcoming scream… red tummy of hers… and death is imminent…
Sentinel (if we count him), then Solael’s, then Dreeg’s. Bysmiel’s is disappointing to me, like Gnomish said, especially because it’s last of three. It could use a buff.
bysmiel could use some backup yea
Def Solael. I think he’s the first boss you face that has a blatant hitscan ability, and boy does it hurt when still low on relevant resists.
Yea Solael’s is the most dangerous guardian, at least on normal and elite. Not sure about ultimate since I usually do the hidden path when the char is mostly decked out in endgame gear already, so the guardians don’t last long enough to see much of a difference.
I agree. It’s the Guardian of Bysmiel so it should summon a lot of pets. Maybe in waves like Mogdrogen’s pets or when HP reaches certain % or something like that. Even Dreeg’s guardian is summoning cute little eye pets all over the place, but Bysmiel’s got nothing.
#buffbysmiel
second one i never died to others but ony to this one
Usually dreeg cause I always seem to lack poison res somehow while levelling. But Solael can be scary and Bysmiel hits like a wet noodle lol.
I have occasionally died to Dreeg and Bysmiel, but nowhere near the same number of times as Solael.
Only ever really died to Sentinel.
But, out of the 3 guardians, yeah Solael definitely feels harder than the other 2.
anti venom salves? 
just occurred to me, if in some aspects Pusquill might actually be harder than Dreeg
Even if we ignore the the cave’s poison arena itself or the ease of dealing with Dreeg eyes, kinda feels like Pusquil has “more” attacks or more significant attacks like the wave and one of the projectile bursts seem to hurt more than what Dreeg offers?
Guardian of Dreeg used to be far more dangerous when the eyes had like 40 flat resistance reduction. Now they have nothing, not even sunder.
I haven’t died to a single one, but Guardian of Solael is the most dangerous because those chaos pools he uses can rack up major damage fast. Most of the time i have to back off.
For the last 5 years don’t think I ever died to any of them to be honest. Gotta mention that I do the hidden path after lvl 94 all geared up, so I shouldn’t really die there.