(note- I had most of this typed up before I saw you had two choices picked out, so I'll post it anyway, but of those two I pick Reneigh
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I'm one of the few, it seems, who loves a lot of sisterly ladies. It could be because I just like the personality a lot- if I were a villager, I think I'd be sisterly (can come off as gruff/rude but super caring deep down, but I've also got a funny/mischievous side).
My favorite, though, should be obvious... *pokes avatar* Ursala is MY GIRL. I LOVE her eyes, her cute little muzzle, her freckles, her hair, her colors, her expressions... I LOVE that her name is a solid pun. And I just think bears fit the personality well- sometimes sisterlies mention coming off as scary, as a bear might. But bears also tend to be very maternal, just like sisterly villagers! For some reason, Ursala seems really unpopular. I literally do not understand why she's not the #1 sisterly.
Other ones I like:
-Hazel (that unibrow is pure perfection)
-Deirdre (another good pun, plus she's got a cute face)
-Phoebe (she's literally a phoenix- how can you NOT love her? her colors are gorgeous, too)
-Reneigh (I am a sucker for puns, okay? also, she's got a cute, sassy face and pierced ears which are fun)
-Agnes (just love her colors, and pigs are totally underated)
-Paula (she really does look like someone's big sister, and again, bear)
-Canberra (has a sort of doofy but cute face, and is a less common species as a Koala)
-Sylvia (is a mom to a mini-me baby- two villagers for the price of one!)
Normally my list includes Charlise but...

I also had Plucky for a bit (have her Amiibo, wanted Del out ASAP 'cause he would. not. leave.) and she charmed me more than I expected! Her name is cute and fitting for her species AND personality and her house is fun. Here's a couple pics I took of her-