Very solid progress. Nice work.
There's no "best" split, but that's one solid option for sure.
As far as specific routines, this is a solid 4-day plan laid out differently (chest/bis-back/abs-shoulders/tris/abs-legs):
Or if you're feeling extra-froggy, you could use these principles to put together your own plan:
Odds are you'd be better off with a fully pre-written plan for at least the next few months though, until you get the hang of a bodypart split. It's drastically different from what you've been doing.