I think I know WAY too many minor differences between GBA CoM and all the RE:CoM versions...
Anywho, I got into KH through GBA CoM after seeing the US commercial for it... Afterwards, I played through KH 1 and then KH 2 before pre-ordering 358/2 Days for the DS at the time... And the rest can be described as "played all of the US released KH games up until after the PS3 REMiXes since I bought the PS4 REmasters without even owning a PS4 yet"...
With that said, platinuming all of the PS3 KH trochievements was not as fun as I thought I was going to be... All of the Final Mixes (with a small exception of probably KH2FM and BBSFM) felt more of a chore to 100% complete than Jiminy's Journal in vanilla KH2, the 358 and Re:Coded "movies" ranged from being not as good as their DS counterpart to somehow being more boring than their DS counterpart, the sticker trochievement glitch in BBSFM made me waste ~5 hours to work around twice, and the lack of difficulty trochievement stacking in 1.5 almost soured the rest of my overall enjoyment of RE:CoM even though I would personally choose GBA CoM over any of the RE:CoMs...
Regardless, I still love this series enough to platinum all of the PS4 KH trochievements once I [finally] get a PS4 and wait [even more] for KH3... Also, I missed out on that special KH PS4 theme unlike that special KH PS3 theme from before...