I mean, to be honest, there is a mountain of quality difference between Petit Cheval and Lafleur. Yes, the Petit Cheval will make it another 10+ years, but it is just no where near the quality of Lafleur (or Mouton).
Of the high end, Lafleur is my favorite right bank wine. (I've never had a good vintage of Petrus or any vintage of Le Pin, though.) However, Haut-Brion is my favorite Bordeaux overall and can be a little less expensive than other similarly situated in stature Bordeaux (both banks).
There are a lot of left bank wines less expensive that Petit Cheval I would choose above it: Montrose, Cos d'Estournel, Leoville Las Cases, Pichon Baron. And Palmer is a bit more than Petit Cheval but much less than first growths.
Note: I haven't had any major chateau 2012s yet. I'm basing all of this upon older vintages. I have had 2012 Poujeaux twice, however, and it seems to be a decent, probably slightly early maturing vintage.
Edited to add: You are looking for a case. I'm not certain when the other 11 bottles are to be consumed. All of these wines will be in fine form in 2030 or 2033. 2045 is a different story. If the idea is one bottle a year for 12 years starting in 2033, your best bet may be a first growth or else Leoville Las Cases.