Between flanger, phaser, and chorus. I know some people swear by putting phaser or flanger in front of their dirt. But for me, with an MXR Micro Flanger, it was just too subtle in front of my dirt pedals. I just obtained an MXR Phase 95, and currently have after dirt with my flanger. They’re both going into front of amp, which I do have on the dirty channel, but with low gain. And my chorus is in the loop along with delay and tremolo.
I suppose it only really matters if you have more than one of them engaged at a time. I mostly just have the phaser and flanger going into front of amp due to how my board is arranged.