Preference.
which is better

um... the French has much more variaty than the dragon variation of the sicilian, so a comparison between the two is hard to make.
the dragon is at around move 6 I believe into the game, while the French is at move 2 into the game, so the French has the Advance, Winawer, Tarrasch.... and so on for miles... while the dragon containes mainly different attack methods and sacrifices.
I like the French more than the dragon to answer your question with simplicity.

Preference.
which one do u prefer
I have never played either.

The french usually ends up cramped for me, and I find scillians too complicated, so I'm currently playing 1...d6. So far, it's going quite well!

I'm a sicilian killer, and love to see every variation of it. It's a rediculous opening, not developing, full of holes, for what, an extra central pawn?
WHY DO PEOPLE PLAY THIS?
The french I would say is better. But personally I play the principled 1... e5 in response.

The funny thing is that fritz 10 is saying white's better by .8 or so in the open sicilian. White does have alot of potential attacking possibilities for the central pawn.

using chess engines to analyze openings is useless, although what I say does go against opening theroy, it still boggles my mind that the sicilian is so popular. Well I guess it is better then the french if you are going for the full point, being combative & not running into the exchange french.

the dragon was one of the first two openings i learned, the other was the Kings Indian. unknowingly i started playing with two of the most complex and over analysed openings of all time. i play the french now, almost without exception, my fall back is the taminov Sicilian. i havent played the dragon in years, i think the Yugoslav attack is almost a refutation to the dragon and i refuse to play against it. so the french for me
the dragon was one of the first two openings i learned, the other was the Kings Indian. unknowingly i started playing with two of the most complex and over analysed openings of all time. i play the french now, almost without exception, my fall back is the taminov Sicilian. i havent played the dragon in years, i think the Yugoslav attack is almost a refutation to the dragon and i refuse to play against it. so the french is the choice
the yugoslav is not a refutation

"i think the Yugoslav attack is almost a refutation to the dragon and i refuse to play against it." dosent mean dont try for yourself have fun, play the dragon. im gonna stick to my french

dragon or french? hmm... i'd somewhat say dragon, cuz nowadays i play the Najdorf instead. French like closed positions, it's quite tiring to figure outposts for knights. At least for me, though.

If the dragon is almost refuted or at least advantagous to white then obviously it's a risky but sharp choice for black. I think it's fully playable until gm level, and even then it's hard to play perfect in those positions. That's why there is long opening theory: to analyse the strongest ways and perhaps ideas to continue in the middlegames from the dragon with plenty of time to think about those positions at home.
which is better the dragon or the french