Cannot stand the latter three Alola forms. It's such a shame because while Persian and Raticate are understandably kind of ugly, Golem had serious potential to actually look badass and not like someone drove a wrench through it.
It looks like someone tried their hardest to turn a boulder into Mario, what with the silly facial hair. At least it has a redeeming quality, that being a unique Rock/Electric typing which I personally dig. It's basically a big "go away" to Flying.
Now, I love the idea of the Alolan forms. A Pokemon varying in appearance, type and sometimes even abilities depending on geographic location? An idea that's, in my opinion, been long overdue. They're brilliant to me! Hopefully the idea's improved upon in a later installment.
Now then, the thread's question. As for Alolan forms that I like, I absolutely
love Raichu's Alolan form. It goes from being a cool and kinda cute electric mouse to a super adorable one that I can't get enough of. After my first playthrough of Moon, I started again JUST to use this form. I have to say, my heart melts whenever I see it in Pokemon Refresh. Other forms that I really like are Marowak's and Muk's. Apart from shared likes between the two (that being their battling prowess - seriously, they're both amazing in competitive battling thus far), I love Marowak's typing and how it serves as a little homage to the Marowak ghost from Lavender Town and just the Cubone story in general, while Muk becomes a Skittle due to the garbage it eats in Alola, and it's less toxic waste as it is "happy garbage muncher".
Least favourites? Honestly, just Persian. Looks like the end result of getting too close to a wasp's nest and it became a boring mono Dark type with an annoying ability in Fur Coat. It's just downright ugly.
edit: add Dugtrio to my least favourites because even though Ground/Steel is amazing typing, Dugtrio does not make very good use of it. That and it looks weird with the hair, and competitively it's just "meh".