So that this isn't a ridiculously short post, I'll go season by season:
Adventure: Taichi! Obviously he kickstarted the goggle boy archetype, which is cool, but I'd also argue that he doesn't entirely fit the mould since he's actually pretty smart sometimes, and that's rarely a bad thing. Additionally, and this is very cheesy, but: now that Matt (um, my brother, that is) has grown up into a proper person instead of just something gurgling and squishy, rewatching basically any scene involving Taichi and Hikari hits my buttons in a way they didn't before. That time when he was stuck underground with Koushirou and helpless... oh man. Speaking of Koushirou, he's right up there too; I swear his backstory and personality were written purely to inspire hugs. I also like Jou and Sora, and Yamato had his moments, and crap that's half of the main cast already, isn't it?
02: Not sure. Most likely Daisuke or Iori. Daisuke just on principle (and because anyone who manages to save the world with the power of shallow characterisation deserves at least some respect), Iori because come on, he is cute. I really liked 02!Takeru at one point, but I find the others more interesting now.
Tamers: TAKATO. Because adorable. ♥ Also Guilmon and Jen (who I've again been liking even more on recent rewatches) and Terriermon and Ruki and Juri and the composite character Hirokazu+Kenta and Ryou if you count game canon
Frontier: Takuya is cool and all, but I'd have to go with Junpei.
Savers: ...I've tried to watch more than six episodes, but. :(
Xros Wars: Um. I started to get attached to Zenjirou, then he left a couple of episodes afterwards.
Hunters: So far, Tagiru is all right and Yuu is a lot more likeable these days. Please don't spoil me! I'm like five episodes behind!
Day 02: Favourite character.
Day 03: Which digivice do you like best?
Day 04: Favourite digital monster.
Day 05: Favourite crest.
Day 06: A couple you wish existed.
Day 07: A couple you can’t stand.
Day 08: Favourite couple.
Day 09: Favourite friendship.
Day 10: Favourite season.
Day 11: Who do you think wore the goggles best?
Day 12: Least favourite digital monster.
Day 13: Least favourite character.
Day 14: Least favourite season.
Day 15: A character you’d be best friends with.
Day 16: A character you would not get along with.
Day 17: Best dressed character.
Day 18: Worst dressed character.
Day 19: A moment that made you happy.
Day 20: A moment that made you sad.
Day 21: A moment that made you angry.
Day 22: Favourite villain.
Day 23: Lease favourite villain.
Day 24: Favourite minor character.
Day 25: Favourite episode.
Day 26: What crest would you have?
Day 27: Would you ever have a Digimon for a pet?
Day 28: English names vs Japanese names (Which do you prefer?).
Day 29: Favourite quote.
Day 30: An unpopular opinion.