Just wondering what is the best console to play on for this game. (So many different types on the leader board )

The Wii version is technically the fastest version. It can skip end-of-day cutscenes, saving about 30 seconds per day. There are some other version differences, some in favor of Wii, some in favor of GC. Most people prefer to use whichever version they're more comfortable with, so I would recommend going with whichever version you've played the most, and are most familiar with.

Also, I don't know if you're including region differences? PAL GC is a lot slower due to a slower framerate. JP is about 5 seconds slower than US, because Secret Safe weighs 85 instead of 40. PAL Wii and US Wii are pretty much identical, I believe.
TLDR: US is probably your best bet, regardless of if you play on GC or Wii.

Are there any glitches in the JP version that's not present in the US one? The top three times use that version, but it may just be a coincidence.

Wheres the pikmin speedrun discord?

There is a link to the Discord under the "Follow" settings tab above. Just click on the Discord logo for the invite - it's a little hard to see with speedrun.com's layout.