"Best" is really only an opinion. There really is no "best", as everyone's needs are different. I have been using his 9.051 navcore for a while now, as it suits my needs. That thread was started by bmwdriver - the author of the modified navcore.
The compatibility chart tells you which maps are compatible with each navcore:
As you can see in the column 9.0xx, which corresponds to 9.051, you can use any v900 map you want, as they are all compatible with the 9.051 navcore. Generally it is preferable to use a full featured map such as 900.4602.