Whether which one is better depends on what you are looking for. The DS and subsequent version uses a new, more direct and literal translation.

The SNES and PS1 version uses Woolsey's localization, which a lot of people have fond nostalgic memories of. I'd say the real defining difference between the two is the translation. The DS version also suffers in the music and general sound department by virtue of being a handheld, but again unless you are a stickler for perfect audio then you'll likely not even notice. There are some odd aesthetic choices in the DS version and later ports such as an odd color filter that slightly yellow-washes the game, but not to an annoying point or anything, but it's worth noting.

The bestiary is just a trivial add on that doesn't mean anything and the Arena of the Ages is arguably the worst of the DS extra content, so it's not really a big loss to not have it. The FMV sequences being removed is an odd choice and a bit disappointing, but not a big deal.

The only thing the Steam and mobile port are missing from the DS version are two of the FMV sequences, the bestiary and the Arena of the Ages. The DS, Steam and mobile versions are virtually identical.

I don't think Chrono Trigger really has a definitive version.

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