I haven't tried FF4 DS but something about Golden Sun has just captivated me. The music was just simply suberb for starters and I could really get an in-depth feel for the characters. I just enjoyed it drastically and the sequel was far impressive...unfortunately I haven't completed it, I probably should pick it up again and play it, but if I did that I want to play the original all over again first to be able to get back into the spirit and fully remember the storyline etc.
Final Fantasy 4 DS I will definitely buy however, I played through the first half of the original and I think it's better to just wait for the DS version so that it will feel entirely new to me.
I would of loved to of seen a new Golden Sun title either on the Wii or DS, I guess the developers have just moved on.