Go with Four Seasons Sayan, particularly if you want a pool suite. Sayan is much smaller by room count and more personalized and spacious than FS Jimbaran Bay, where the relatively high room count makes it feel big and the rooms (villas) feel like they are on top of each other. Don't worry about weather in Ubud in December; it's fine. You will be much closer to--in the middle of-- the cultural sites, feels, and experiences if staying near Ubud.
Amankila is my other favorite in Bali. You won't feel like you're missing out in an Ocean Suite, because you don't really need a pool (six stays, no pool yet for me), but if you had only a garden view I could see where it would feel like you're at the kids' table.
You could always split between amankila and amandari. I've done that and enjoyed it. But my personal preference is FS Sayan over amandari when selecting a resort near Ubud. I find them quite different in architecture and feel, with Sayan more to my liking, and I consider Sayan a better value--especially if you want a pool villa.
All that said, there are many top resorts in your price range that I've never stayed at so can't comment on. And there is no "best hotel in Bali." It's all a matter of taste and what's important to you.