I know he got kind of a cool reception around these parts but I always really dug Astromons from Taro's first episode.
I mean, seriously, it's like a 1970s Biollante pre-make! I've got a really sweet Ultimate Monsters figure of him sitting on my desk - I would consider every figure from this line that I own among the best of my entire collection but the Astromons figure is something truly special. I'm not sure if it's the figure itself or the amazingness of the design! Though I'm pretty sure I'm in the minority around these parts, the insanity of these designs are why I tend to like the Ace/Taro monsters more than many of those from the rest of the series.
It's kind of a shame to think that the franchise has kind of since surpassed this brand silliness. Like, there's still comedy and bizarre monsters but I'd have a really hard time imagining a monster as patently crazy as Giigon or Mochiron being revived in a current work (even though I have SO MANY IDEAS for how Mochiron AND Minami could make a comeback XD).