Honestly don't have a plan yet, but I guess I could do either. Probably Colosseum.

I have:

• a childhood GameCube with an ODE (so I can play XD, Colosseum, Channel, Box)
• also childhood GB(A) Player attachment
• my sister's model 1 Game Boy Advance I just have now
• GBA-to-GC Link cable I got from a friend
• GBA link cable I just ordered from AliExpress for like $7
• childhood copies of Ruby, Sapphire and a non-childhood JP copy of LeafGreen
• Everdrive flashcart for the GBA so I can play and trade technically infinite amounts of the gen 3 GBA games although it can't be used with Box, etc. since it needs to be on to select a ROM and I think most of those GBA-to-GC features require the GBA to be off

I think that's enough to get everything that gen, even stuff like the eon ticket since I an either dump the save to PC and distribute into the games via emulation or the flashcart can actually emulate some e-reader functions. I could technically speedrun Emerald on the flash cart without wiping my Emerald cart to trade the gen 2 starters too, I think. Same thing with FR/LG. I think I can get a legitimate JP Celebi by playing JP Colosseum on my GC and then transferring that to JP LG and then trade that to Emerald or whatever. I gotta' install new batteries in the carts. I think all I'm lacking is the wireless gba adapter if I wanna' do pokeblock stuff in FR/LG/E which I'm not sure if that's needed at all, even for the ribbon/contest ribbon stuff. Can probably emulate that part if needed although I'm trying to avoid doing anything on PC if I can.