Hmm I can't really pick one so I'll just post my top 3:
Digimon Tamers:
This is without a doubt the best season of Digimon. The main characters (Takato, Jenrya, and Ruki) all have an even amount of development and none of them are left in the dust, unlike Adventure or Frontier. It starts out like a normal season of Digimon. Here's the kids, here's the evil Digimon, kids win. Then it becomes more darker and has more thought in it especially at the end of the Beezlebumon arc and throughout the D-Reaper arc. There's also some flaws, like having useless side characters that do almost nothing (I'm looking at you Marineangemon), but I enjoyed it.
Mobile Suit GUNDAM 00:
I'm going to be honest, I haven't seen any other Gundam series other than a few episodes of SEED, and this was my first time actually watching a Gundam series. Anyways, I loved the animation in this. It's just beautiful. The plot is interesting to think about. Eliminating war via armed interventions. I don't really see much character development from Setsuna though and he seems to be a bit bland. Allelujah, on the other hand, is very fun to watch due to the multiple personality disorder. One minute he's calm, the next he batshit insane. But this is only for Season 1 as he turns into a whiny bitch in Season 2. Now while I loved Season 1, I didn't enjoy Season 2 as much. The only thing that I can say about Season 2 is that they made Saji and Louise something more than just civilian points of view and made them active parts of the storyline, instead of a little subplot.
Tenga Toppen Gurren Laggan:
The style of art is different than what I was used to, so it was a bit of a surprise when I started watching it. I'm not saying that the animation is bad. The whole art style is unique, but sometimes it does become a bit erratic during a few fight scenes. This anime balances humour, action, and character pretty much perfectly. Simon has some of the best character development that I've seen in an anime, particularly during episodes 9-11. Scale-wise, the end of TTGL is bordering insane. Throwing galazies and combining them into an attack with the energy of the Big Bang is something that even DBZ didn't even touch (even though they both did tamper with space-time rips). The only gripe that I have with this anime is during the final arc, when Super Galaxy Dai-Gurren was in the space-ocean that was made of compressed space, because compressed space is an oxymoron as space cannot be compressed. But once you enter galaxy throwing, you can ease the laws of physics.
Anyways that's just my two cents about my favorite 3 animes.