The one with the most experience.
We can rule out the socially awkward shut-ins who have never seen a dick outside a dounknshi (Marine, Pekora, Gura et al).
Sora and AZKi are probably the best in Gen 0. Suisei likes to pretend she is experienced, too, but screamed in terror when AZKi showed her a picture of a real dick.
1st Gen, Fubuki has probably had a dozen different dicks in her mouth. Matsuri is super jealous and wants Fubuki tonteach her her ways.
2nd gen, Subaru is the normie who pretends she doesn't know what the other girls are talking about, yet is the only one who has sucked a guy off before. Okay, there's Shion, but that was compensated dating and the guy wouldn't take 'No' for an answer. She sucked at it.
3rd gen, Rushia's married. She has only ever sucked one dick, her husband's, but she has done it a lot and knows all the little tricks. Probably the best dick sucker in hololive, but she'll only do it for thst one man. She likes to tease, but never goes all the way.
4th gen is clueless. Even Coco, who hates swallowong and prefers to take it up the ass.
5th gen, Lamy can't swallow without throwing up from excessive alcohol consumption. Polka knows what she's doing, but she's fat and hasn't had a dick in years. Botan prefers giving handjobs.
All the Indonesians are virgins in every hole by necessity (fingering doesn't count, has to be a dick), because living in Indonesia, premarital sex risks a caning, and not the fun kind of caning. Also a stoning, but that'd technically be illegal.
Holo EN, Amelia had a boyfriend, but he dropped her because she was just bad at gargling his dick. Kiara has done quite a bit during her time as a flight attendant to finance her trips to Japan. Calli's a virgin. Gura and Ina are shut-ins. Kiara wins by default.
Holostars, Rikka has sucked off every other dick in Holostars and his own. Second only to Rushia in quality, even if he's being violently throat-fucked by Shien. Never misses a drop and eagerly swallows, knowing fully well that he'll be bitchslapped by the others if he performs poorly.
