I found doing weighted negatives helped my regular weighted ones a lot. It gets you used to how the weight acts on your body.
On a bodyweight forum I saw lots of people trying to get chinups to a level where they can pass fitness tests for military or being a fireman. These tests often have rules, it would usually be chin to the bar -so it would be foolish to go to a chinup contest and start doing chest to the bar ones, and unnecessarily tire yourself out and lower your reps.
But if you are training for strength you might want chest to the bar, it is an easy way to increase difficulty and could lower your reps into a range you prefer. Conversely if you can only manage 2 chest to the bar chins you are probably better sticking to chin to the bar for now.
You can see some rules & records here
they have separate ones for chins, pullups, 'leg assisted pullups'