It’s Ark-ee-us for me, because I think the hard C resonates with the words “arc” (like the shape of Arceus’s golden adornments) and “arch” (as in archangel, archon, etc.) and, as Pikachu315111 pointed out, it’s consistent with the RKS System ability. And to be honest… yeah, ever since someone pointed out the “arse” thing to me, I kinda can’t unhear it. :/
On a wider note, I went through a video of Pokédex 3D Pro’s pronunciations in order to compare which names I say differently from what I presume are all the official pronunciations for everything from Gen 1-5. The ones that stood out as the biggest differences were:
The Nido family: P3DP seemed to pronounce the I as a long E sound, whereas I say it as a short I sound. Nih, like in “knitting.”
Omanyte and Omastar: This pair was kind of funny. I do say Omanyte the official way, as a homophone of ammonite. But with Omastar, even though it’s inconsistent, I feel more drawn to pronouncing it with a long O sound, as Oh-muh-star.
Chinchou: I seem to flip-flop on this one. Sometimes I say the official Chin-chow, other times I say it as Chin-cho.
Yanma and Yanmega: I say the first syllable as “Yahn” (sort of like “yawn”) instead of “Yan” (rhymes with can)
Nincada: I pronounce it as Nin-KAY-duh, as opposed to Nin-KAH-duh. Frankly, I’m confused by the official pronunciation on this one. Perhaps it’s a regional thing, but I don’t think I’ve ever heard someone say “cicada” with anything other than a long A in the middle.
Aron: I say Ahr-on instead of Air-on.
Roserade: I say this with three syllables rather than two. Officially, it’s Roze-rade, but I say it more like Ro-zer-ade.
Wormadam: I pronounce it like “madam,” as in, the formal mode of address for a woman. I’m kind of surprised that isn’t the official way of saying it (instead of Wur-muh-dam), seeing as how Wormadam can only be female.
Mismagius: I pronounce the middle part like “mage,” and I firmly believe that’s how it should be said, because the official pronunciation is atrocious.
Gabite and Gallade: I put much more emphasis on the first syllable than the second for these two, saying GAB-ite and GAL-ade instead of guh-BITE and guh-LADE.
Carracosta: I flip-flop a lot when it comes to that O sound. Sometimes I say it like “cost,” other times I say it like “coast.” I dunno which I really prefer. Also, on a related note, it kinda bugs me when I compare this one with how I say Karrablast. Naturally, I pronounce the first syllable in Carracosta as “Kahr,” and the first syllable in Karrablast as “Care.” But if I stop to think about it, I feel like it should be the other way around; the one that starts with C should have the “Care” sound, and the one that starts with K should have the “Kahr” sound.
Druddigon and Hydreigon: The official pronunciations seem to say the last syllable like the word “gun,” but I say it more like the word “gone.”
There were a handful of others where my pronunciation drifted slightly from that P3DP was saying, but I didn’t think those were significant enough to mention.
As for Gens 6-9, I’m not actually aware of how all of those names are pronounced. I’m familiar with a few from various anime clips, though, so I’ll at least point those ones out.
Skiddo: The official pronunciation with its 23 skidoo nonsense is cursed and I hate it. I say it like Skih-doh, as in, “skid” + “kiddo.”
Furfrou: I say it as Fur-froh instead of Fur-froo.
Diancie: I actually only realized this the other day when watching the Pokémon Presents video, lol. I guess officially it’s Di-AHN-see, but I say it as Di-ANN-see, like the name Diane.
Dewpider: The official pronunciation I’ve heard sounds kind of like the word “Jupiter”? That feels really weird to me. Doo-PYE-derr, rhyming with “spider,” is surely more intuitive?
Silvally: Whereas in contrast to Dewpider, while the official pronunciation here makes more logical sense (the last part is pronounced like the word “ally”), I’ve been saying the last part like “alley” for so long now that it feels much more organic to me that way.
Solgaleo: I say this one like Sol-GAY-lee-oh, rather than Sol-guh-LAY-oh. I can see an argument for either case; my version was certainly derived more from the “leo” part, like the astrological sign, whereas the official pronunciation has a fitting resonance with the name “Galileo.”
Zacian: I say this like Zah-see-an rather than Zah-shee-an.
Regidrago: IIRC the anime pronunciation said the third syllable as “dray,” but I say it as “drah.”