What is the best chorus pedal?

That's a toughie, since I haven't heard the song.

However, I did look up his guitar rig, and I have a few ideas of how he could have gotten that sound.

One option could be using a combination of ElectroHarmonix Small Stone or Poly Chorus with the Boss RV-5 Digital Reverb/Delay.

Probably did it with the Boss Roland RE 20 Space Echo Delay Reverb Twin Pedal, though. Apparently it combines echo with a bit of modulation, similar to how a tape echo adds a little extra somethin' somethin'.

Something to consider is using a parallel fx loop of some kind to add effects like that in the background. Again, no idea if it's the sound you're looking for, but if you want a very clean strummed sound, for instance, with a layer of echo/chorus wash in the background, then you would use a parallel fx loop. Many amps don't have anything like this, but it would look something like this -

fx loop out -> volume pedal -> chorus -> echo/verb/delay -> fx in

The idea is that you can use the volume pedal to "blend in" some of the sound at will... and keep the echo and delay tails for notes, but be able to cut off what you feed into it.... or would allow you to create volume swells, ie synth/pad sounds.

To make it happen when your amp doesn't have an fx loop, you could do something like running your guitar into a mixer, with the fx loop out going into the pedal sequence above. When I've done it, I run my guitar into my "normal" effects first, ie wah and distortion pedal.

Saul