My Personal Top 6 G1 MLP Characters:
1. Wind Whistler - I've harped on her before but this pegasus mare is awesome. She's an extremely intelligent and often downright cunning pony who often jumps up to be the leader in a crisis. She does have some issues with being wordy / technobable and favors logic over emotions to the point that she's extremely stoic. I just find her awesome as she just doesn't fit with the rest of the ponies at all and would probably be more at home in Star Trek. Given what happened in 'Crunch the Rockdog' where she sacrificed Truly to get a chance of hitting the Rockdog with the heartstone to save everypony else she'd pass that 'Bridge Officer's Test' quite easily.
Closest G4 Equivalent: Twilight Sparkle - if she was mixed with Mr. Spock.
2. Fizzy - This Pony. This pony single hoofedly broke my brain. She's a happy-go-lucky, klutzy, scatterbrained unicorn mare who has the power of creating and controlling bubbles and who has the occasional moments of awesome (like drawing off the fire from the demon trees in the Shadow Forest so that everypony else could escape). She is also the most prominent of the few 'Twinkle-Eyed Ponies' who have gems for eyes. She's pretty much the Derpy/Ditzy Doo of G1.
Then I found out the official canon back story of the 'Twinkle-Eyed Ponies': Turns out Fizzy spent a good bit of her life as an horribly mistreated slave forced to work in a hazardous mine by the 'Jewel Wizard'. She lost her sight but when she was rescued by Applejack (who killed the Jewel Wizard and destroyed his gem throne). Some of the magical gem shrapnel from the exploding jewel throne embedded itself in her corneas and thanks to the gems she regained her sight. Dear feaking gods. It would be like finding out G4 Derpy/Ditzy's official back story is that she was horrible mistreated by an abusive alcoholic father and her eyes are that way because she was once nearly beaten to death before Applejack saved her by killing her father. Yeah. Anyway, I now have immense levels of respect for Fizzy.
Since the original page hosting the comic got overloaded:
Applejack's Amazing Adventure - 1
Applejack's Amazing Adventure - 2
Applejack's Amazing Adventure - 3
Applejack's Amazing Adventure - 4
Closest G4 Equivalent: Derpy/Ditzy Doo
Closest G4 Equivalent: I'm going to cheat here with a fan work - but it fits so well: Blackjack from FoE: Project Horizons.
4. Paradise - She's a pegasus mare in a magical land who loves legends and fantasy and once asked "Why can't my life be more like a fairy tale?". Then again she lives in Ponyland, which seems to be full of slavers, crazed evil overlords, sealed ancient evils all about the place, and a lot of the G1 MLP stories feature near apocalypses. Yeah, I'd want to escape that place and live in a generic happy fantasy land too. She usually is the storyteller or dropping lore exposition. She also has a glorious epic fail trying to hammer a nail.
Closest G4 Equivalent: Going by her card description of being obsessed by legends and fairy tales: Sugar Grape
Closest G4 Equivalent: Daring Do.
5. Heart Throb - A romance loving pegasus mare who is all about sharing love and dreams of meeting her Prince Charming... And she pictures him as a human - which is a bit disturbing especially when the fantasy comes to life and starts reciprocating. She's usually more on the funny side since most of the episodes are action & adventures.
Closest G4 Equivalent: Princess Cadance with a bit of Rarity and... Lyra...
Honorable Mention: Masquerade - This twinkle-eyed pegasus mare is master of disguise, infiltration, and general spying. She doesn't show up much (or does she?) but where she does she has rather interesting skill set and used in plans such as posing as Grogar's second-in-command bray from a distance in costume.
Closest G4 Equivalent: Not sure... Maybe Con Mane with a dash of Dash & Pinkie?