Where to transfer to the subway from the Bx7?

I'll be going from close to the top of the Bx7 line down to the GWB, and then into NJ on a Jitney most weekday afternoons, but people have said it's faster to switch to the subway instead of staying on the bus down to 178th.

Is there a "best" place to transfer (which is fastest, safest, etc.)? It'd either be

* 231 St on the 1 train to 181st
* Marble Hill 225 St on the 1 train to 181st
* Inwood 207 St on the A train to 181st

Does it matter? Is it best to get off the bus as fast as possible, or best to stay on the bus as long as possible? Make sure I transfer to a train before entering Manhattan?