Im planning my first trip to Paris and try to figure out how to get to Maisons Alfort Alfortville station or near it.
On all the website it recommends RER B to Gare du Nord - M 5 and then M 8.
I noticed that RER D runs through Maisons Alfort Alfortville. Is there a reason why the route
RER B to Gare du Nord and then RER D to Maisons Alfort Alfortville is not recommended? This way one has only one transfer at Gare du Nord.
The simplest route would be as you say: RER B train from CDG to Gare du Nord, RER D to Maisons Alfort.
Please note you will need a special RER ticket for this trip from Airport CDG to Maisons Alfort, which is different than a ticket from CDG to central Paris. Maisons Alfort is in zone 3 outside of central paris and you would be traveling from CDG Airport (zone 5) through central Paris (zone 1) and back out to zone 3 to arrive at Maisons Alfort.
The ticket agents at CDG Airport train stations or any RER station will be able to sell you the correct RER ticket when you tell them your desired destination station (Maisons Alfort).