What comes first the chicken or the egg? LOL
Seriously, as a 22KHz switch typically has higher switching capacity and reliability, I might lean towards putting it first in a cascade.
BUT....
Some STBs and switches don't play nice and you may need to install how it works with your switches and STB. Example, the majority of FTA STBs are used with Universal LNBFs (which would be down stream from a DiSEqC switch) and the 22KHz tone may be interrupted when a DiSEqC call is issued. The 22KHz switch may stay latched or return to default port 1. The DiSEqc switch may be committed or non-commited and switch back to default port 1. This varies from switch to switch and STB to STB. I recall some issues with the order of switches or the lack of command repeats to extablish the signal path.
Sorry, no correct generic answer. Just test and see which method provides a reliable signal path.