Both are excellent. The 24 II is a little sharper. But really, it comes down to focal length - is 24mm wide enough to frame what you need? Architecture sometimes needs a wider AoV. Personally, I'm very pleased with my 24mm...

EOS 1D X, TS-E 24mm f/3.5
L II, 2.5 s, f/8, ISO 1600, +8 shift

EOS 5D Mark II, TS-E 24mm f/3.5
L II, 1/60 s, f/11, ISO 100, +10 shift

EOS 5D Mark II, TS-E 24mm f/3.5
L II, 1/2 s, f/8, ISO 100, +12 shift