Is SoI meant to be a bad game?

I think it's mainly just because it's a GBA game as opposed to a main console entry. The game quality naturally goes down in comparison simply due to the restraints of the handheld console. It's not a bad game for the GBA, just bad in comparison to other home console games if that makes sense.

EtD, because it's a direct sequel to YotD.

Also, why is it "pick your poison"? Is SoI meant to be a bad game?

i enjoyed Season of Ice personally, i was a bit confused by that too. although it had the same problem every Spyro GBA game had where my depth perception was off (thus i didn't know where i could glide sometimes) because of the overhead view

I can't remember but the events of EtD and how that game starts is basically right after the old dragon kingdom (forgetten worlds) finds peace.  It's not talked about in the cutscenes, and I know on teh wiki's it says it takes place "shortly after YotD" but I don't know what the source is.  Might be from the game manual.

Also, why is it "pick your poison"? Is SoI meant to be a bad game?

Although if I have to choose between your two options, I guess Season of Ice since it wasn't a buggy mess and didn't (IMO) single-handedly kill the OG Spyro franchise like Enter the Dragonfly did.