I've worked with same kind of presets now for the last couple of versions of FM. One does the players extremely professional, able to reach the potential in a shorter amount of time, more loyal (depends one various factors in FM20 but if a player get unhappy just try reason with him in a private chat and normally he will drop his issue), gets match fit just after 1 day no matter how congested the fixture list is and so on. Works like a charm, I especially enjoy buying young gems which are on free transfer while I manage lower league clubs. The other preset I tend to use if I for example would like to try to achieve a unbevlieable result, f.ex a league one/two team winning the FA cup or some thing similar.
I am sure there are ways to improve my presets, but I've found my way so here they are. Enjoy them or not...
Professionals.json
SuperFit.json