For me, I use the BEX-CE / BTX / Extended 3025-57.
Includes several new FPs, Clan invasion, new nations, like the FRR, OWA, The new, advanced mechs and weapons only appear at the correct time, etc.
Very stable, with plenty of other-mods working with the core system (improved/extended contracts hubs for example).
Is the one that respects more the Lore and time progression by a wide margin.