I just finished Professor Layton and the Curious Village and want to go and get a new game. Although the next game is the Diabolical Box, I also really want to play The Unwound Future. What do you guys think I should do?

Buy both. That's what I did. XD But if you only have the money for one, I'd say Diabolical Box, even though it doesn't give you the Clive/Legal experience. Or you could consider the Last Specter, the prequel of the series, which is also excellent..X3