Like C said, if you're looking solely for one game then just grab the original on the SD console you're purchasing for. Unless it's a real remake - like Kingdom Hearts 1.5 HD ~ Kingdom Hearts Final Mix - you ought to go for the cheapest route available.
However, I personally have ordered a copy of Kingdom Hearts 1.5 HD ReMIX and I'm only getting it for KH1FM though it hosts Re:CoM full game, and 358/2 Days in cutscene format. It'd be silly of me to do so; I already have KH1FM for my PC which plays at 100% speed around 99% of the time. However, I do get personal joy from owning the latest addition of a game. It's a quality of a consumer that the big business people know to take advantage of. If you're worried about playing an outdated version of a game, then yes, shoot for the HD collection. If you don't care for the "latest version", go out and order that PS2 version! It's SO MUCH CHEAPER than the HD recollection.