I think the rainbows were fine design-wise, but looked especially good on Pokémon with simpler color schemes (like Arceus and Shuckle). They were repetitive and a bit disappointing to open compared to their colorful counterparts (for me, anyway), but from a pure design perspective they were okay. Nothing stellar in most cases, but okay.
Gold terras (and most other gold cards) are just actively bad from a design standpoint. Nearly every color clashes with the harsh yellow-gold they like to use, and they don’t alter the colors of the Pokémon or items to make everything cohesive. This is especially apparent with Pokémon like Charizard, where the orange of the body and gold of the card clash and become a muddy mess.
Say what you like about the hats, but the awful color schemes of the gold cards have always been a sticking point with me as a professional illustrator- these basic things like color cohesion really shouldn’t slip past the drawing board imo.
Terra type Pokémon look so much better in their normal card format, where the colors are actively taken into account and the crystallization has a chance to shine (pun intended).
Gold tera just looks horrific to me unfortunately. So much stuff in the way of the actual Pokemon. I don’t like rainbow rares, but at least the Japanese ones from the SM era usually have great texture patterns. So that’s 1 redeeming quality to 0.
I’d say both but at the same time i’d rather get CLEAN looking rainbow rares (it’s just a clean pokemon outline + rainbow colors) than those gold ones…
I dislike Rainbow rares because they clogging the MasterSet slots and i have to buy them and they more expensive than most of trainer gallery/full arts despite not being anything interesting…
There are cards with both of them that i don’t like that much but also a lot that i think are really cool ones, so exactly like with other card types too. Great rainbow rare cards are great, great tera cards are great, great art rares are great and great ex cards are great. Everyone can ofc do as they wish but i get much more of it when i try to find the good things in different card types or gens rather than focusing on which is the worst, ugliest or most disappointing, if it isn’t that good i can choose to just ignore it and if i like it i get to enjoy it