I think my favourite is The Hunt, followed closely by Blue Planet 2, and then in third probably Dynasties, which was really great despite being quite short. I liked the new format, although it meant it focused more on famous species and not much by the way of quirky, little-known taxa.
Just running through a list of the ones I have watched in chronological order of their release dates:
Life on Earth: Liked this one a lot when I was a kid and watched them almost on loop at times. It's a shame the cameras weren't developed enough to convey the behaviour in greater detail because some of it was astounding.
The Living Planet: Again, quite old, but some great sequences and probably my favourite when I was a child.
The Trials of Life: Another great one that would have been welcome round about now with better quality of footage. Especially remember the chimpanzees hunting the colobuses because it spooked me a bit...
Life in the Freezer: I was obsessed with Antarctica for about a year due to this one. I made a pretty extensive school project on it, with illustrations and maps and all, and drawings of all the seal and penguin species. Watched it when I was 8 or 9.
Private Life of Plants: Going into this one I was kinda skeptical, as I was now 11, but I actually really liked it, although it didn't begin an interest in plants as the previous one did.
Life of Birds: Also one of my favourites, though not enough to engross me in birds, I was too far down the rabbithole with felids. Some fantastic sequences, especially the lyrebird sequence, which was rather funny.
The Blue Planet: Got really interested in orcas after this, but otherwise kind of washed over me. I don't know why, but I preferred Blue Planet 2 than its prequel. Probably the greater variety of organisms depicted, better camera shots and stronger conservation message.
Life of Mammals: The series that sparked my interest in felids again. I absolutely loved the 'Meat eaters' episode, the omnivores one was great as well, and 'Food for Thought' was also memorable.
Planet Earth: Possibly the most famous of them all until a few years ago, I really loved Planet Earth, with all the different ecosystems. I think this was the peak of my interest in wild animals, because I had just started to use the computer in earnest. It wasn't my favourite though, although I continued to watch clips from it on the now non-existent BBC Wildlife website for a while after.
Life: Especially liked the bowerbird, humpback whale and grebe sequences from this series, and I think I must have watched the mammal and bird ones in their entirety at least 7 times each. My favourite until The Hunt.
Frozen Planet: One of the less memorable ones for me.
Africa: Liked this especially due to the long leopard sequence involving a juvenile repeatedly falling out of a tree
Life Story: I remember two sequences from this one more than any others: the kangaroo fight and wolves chasing a bison mother and her calf. The latter was more nail-biting than the tensest of the sports matches, I have been trying in vain to find it for a while now on Youtube but can't.
The Hunt: I think this series automatically qualified itself as my favourite by beginning the entire series with the most astonishing leopard hunt sequence ever made bar none:
.
It solidifies its position with an amazing orca hunt, tiger hunt sequences, possibly the best polar bear hunt ever filmed:
BBC One - The Hunt, In the Grip of the Seasons (Arctic), An aquatic stalk as well and to cap it all off, the most badass hare in existence:
BBC One - The Hunt, In the Grip of the Seasons (Arctic), The Hare and the Arctic Wolves.
Planet Earth II: I don't think it quite lived up to the hype before it, but still an amazing series. The snow leopard sequence was really nice, and although I was disappointed by the lack of leopards

, it was great all round.
Blue Planet II: The best underwater documentary ever made, without a doubt. Only topped by The Hunt on my list, I especially loved the Antarctic sequences, the enthralling octopus sequence where it disguises itself to fend off Pyjama sharks and the whale shark sequence.
Dynasties: Really nice, I really felt a connection with the animals which can't be felt in the others generally due to generally short sequences where names are not divulged. I especially liked the lions one despite the fact that I'm not a great fan of lions generally - it was probably the most thrilling one with some really interesting behaviour at times. Occasionally the anthropomorphism was cringe-worthy, but mostly great filming.
Our Planet: Only watched these ones once due to the fact that I don't have Netflix at home. Great, with some shocking scenes on the climate change front, but still focused on the animals. Don't really know what to think of it if I'm honest.
Seven Worlds - One Planet: A very striking series, often with lots to say on climate change, but still keeping the sequences novel and intriguing. Especially like the Pygmy three-toed sloth sequence.