I also agree about La Roja. In general, Jolly Pumpkin is among my favorite US breweries, but La Roja is just not a good Flanders-inspired sour ale. In addition to the assessments above, it comes off with a strange woody quality that is not beneficial to the overall character of the beer.
La Folie is my favorite, followed by Rodenbach Grand Cru and Vintages.
Ryane is right on about the base malt. There are so many other elements in the making of this beer that will exert a much more noticeable influence on it.
Although there aren't a lot of commercial options for homebrewers, I'm not a big fan of the Roselare blend. Without putting it through a few generations first, and then really encouraging it to sour along with much age, it just doesn't do much to excite me. If you can get a hold of it, I'd go with Bugfarm or the Flemish blend from East Coast Yeast if possible. (Also, a question I see a lot is whether to ferment clean, followed by a bug blend in the secondary vs primarying w/ bugs. Definitely Primary with bugs, especially if you have to go the Roselare route.