Speaking with my ‘work hat’ on (leader manager at Exodus), if you wanted to work in France you would need your International Mountain Leader (IML) trekking ticket, plus either CTC or SMBLA biking award in order to be legal.
Elsewhere in Europe, the situation is less clear cut, but pretty much all companies would require you to have a first aid ticket and a UK mtb qual, which even if they’re not recognised in the country you’re considering working in, would at least show that you had attended a UK approved training course, and passed an assessment.
I’m biased towards the CTC award (as I work for them as a leader trainer), but at present neither CTC or SMBLA are recognised as the UK National Governing Body (NGB) award, and consequently both are equally valid.
I’m afraid my knowledge of MIAS award is less than perfect, and suspect the other two are more well known as PaulB pointed out.
Hope this helps!