1.24x is a newer version...
all older file versions can be opened by 1.24x,so it makes it the best jj2 version.

And I haven't seen any 1.24x costume levels in J2O O.o
I do all my levels in 1.24 even converted the 1.24x levels to 1.24 ones.

Well for XMas i make levels in 1.24x...