As far as art style and voice over Victoria is my favorite. I could listen to that voice all day long, dat face and dat body are top notch.
HOWEVER
As far as personality and her Yandere level of mental disorder goes, she is the most fucked up of them all. From her dialogue and mentality as far as she is concerned, all she needs is your body, so you might as well be a lobotomized sex doll, and she would be completely fine. Also her uncontrollable murderous tendencies stem from this, revealing her lack of empathy and pretty much psychopath nature.
To put it frankly - regardless of her looks and voice, if that girl ever approached me, she would receive a bullet between her eyes and her body would be fed to the wolves in a dark deep forest, just as a future investment on my part as far as life expectancy and survival go.
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Now, the most "normal" of the bunch I think would be Dipledenia , a.k.a > the safest choice.
First off quickly about her looks and then straight to the more interesting part > mentality. Her looks are appealing to me, she is the petite beauty, but still has a good build. Her voice is a bit more solemn but from what we can see, she clearly is not fully grown up adult yet.
There is a potential for her to become a very very sexy laaaadieee ... oppah Gangnam style..... ehmm *cough.. right, back on track !
Her Yandere vibes are not really yandere to be honest. At least from my perception and the way I look at it her story gives us a good insight into her character. She was in a deep love, which was lost (dont remember if the guy died or broke her heart), and she was scarred for the long term. Her story and character are sad yet sweet at the same time, as after you unlock her H scene and such there seems to be a nice happy ending to her sadness.
She might be overly attached to you, but she doesnt have those "ima gonna murder ya" wibes. As such her psychosis seems of the different type. Dont know the exact technical term but its the one where a person grows overly attached to someone or something, and once they latch onto you, you become the center piece of their universe. Good thing - extreme loyalty and faithfulness, Bad thing - stalker-ish behavior, emotional dependence and the risk carried with it, as well as unpredictable behavior if mindset is challenged by outside source. As far as these 4 are concerned she is the "Safest" choice for long term survival.
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Lavender and Convalaria (in wiki named as: Lily of the Valley) are pretty much similar in their behavior patterns from what we can see, but quickly about the looks. If we disregard the fact that Lavender has oversized head on her first artwork, and as such assume she aint suffering from Dawn syndrome, she is your classic Loli baba > A full fledged adult with the undeveloped body of a child. A legal Loli so to say... calm down officer, no need to pull out that gun. From my experience girls with modest build and small breasts tend to be more sensitive then big bubbly girls with D+cups, but then again that doesn't apply to everyone all the time. Long silky hair, is a massive + in my book. Voice is good enough.
Lily on the other hand is the exact opposite. A mind of a child in a fully grown up body of a adult. She has the curves, she has juice and da mojo. What is a bit off putting due to her personality and feeble mind, might be her facial expression and her unfocused eyes. But thats not so horriblei n the end. Long nice hair, and fairly sexi though a bit grindy voice. Approved.
Now then lets take a look at their mental state that is... their Yandere factor.
Lavender seems rather intelligent and able to come up with intricate plans. Lily on the other hand is of more ... simple mind (she is stupid, not dumb or uneducated, literally stupid, as in: low brain function). Both of the exhibit a strong emotional connection and in their own minds "bond" with you. This is the usual type of yandere where the love is so strong it breaks into psychotic paranoia, possessiveness and overall develops into mental disorder rather nicely.
Still the nature of their disposition is one of the type - where if played correctly, you can easily work around with them, and even have them do you bidding while maintaining relative safety and solid chance of survival.
Whereas Victoria is plain and straight a murderous psycho/sociopath (she might have been born that way, she might have become like that later on, matters none, the end result is the same), these two are mentally fixated upon you as the center of all their actions, thoughts etc. As such for them the fear of loosing you is a good gap stop for not just axing you down for the lolz. Of course should you perform actions that would play into their paranoia and mental disorder they would most likely be unable to control their own actions, kill you and then weep and most likely commit suicide as the center of their existence would no longer be there. As such with proper actions, words, emotions etc it would be possible to steer them in the right direction. Not control them > Remember, these girls are unpredictable to a degree and while you may try reason and logic, with what to do how to act etc, any sort of trigger, anything to act as the catalyst, and the Avalanche rolls down on you.
Now, of course there are some differences between those two, but as far as their psychosis goes, I think they are pretty similar. The differences stem from how they think, act, and and expose their emotions. Now If I were to rate them, Lavender is a bit safer choice simply because her erratic behavior is a bit in check as she tries to keep up her "your lovely cute dependable Lavender chan chuu ~ " image going, which might not be necessarily fake, since we know nothing about their upbringing. To put it bluntly, she weighs her actions before acting.
Lily on the other side..... well just seeing her H scene, plus the fact that her mental capacity is that of a 6 year old, should tell you enough. As such she is more dangerous, since while not necessary "evil", she doesn't think about the outcome of her actions. She is the person who would feed you poison happily, not knowing its a bad idea, just to understand once you are lying on the ground in spasm with bloody foam around your mouth. This childish undeveloped mentality is what makes her more dangerous than Lavender, though on the other hand it would be easier to "control" her, since she would respond to certain educating and training stimuly much easier (no kinky stuff !... ahh who am I kidding, it also includes the kinky stuff but thats not the point.). Hyper sexuality is a well known outcome from people suffering certain mental illnesses like bypolar personality dissorder and such. If you take a look all 3 of these girls are hyper-sexual, with the exception of Dipledenia. Now in comparison to Lily, Lavender has the mindset of an adult and while she seems a bit scatter brainish due to her overburdening fixation on you, she is by no means dumb.
It literally comes down to the pick. Which poison will you take ?
As for Victoria - you might be able to steer her actions a little bit, but as with all sociopaths / psychopaths, its extremely dangerous, unreliable and way to risky. As I said at the beginning - would not dabble with this one.
While I would like to go even deeper into this, it comes to the point where sheer text is not enough and a proper conversation would be necessary to transmit all the information. However I think this is a good summary as far as they my thoughts about them are concerned :P
Now you are free to disagree, this is purely my thought on how I view them and perceive their individual