～の中で are the same.
When used to compare something within an explicitly stated group, as in your sentences, the meaning is identical and they can be used interchangeably. (See below for exceptional cases where the group is not explicitly stated).
～で in this case is just an abbreviation for
～の中で. According to Hamano & Tsujioka (2011), "by using the spatial word 中 (inside) in an abstract sense, you can specify the group in which you are making the comparison". Their examples show the use of
の中 as optional. For example:
Suzuki is the best in the class at English.
There is at least one exceptional circumstance where you should use the full form の中で and that is when the group to be compared is referred to indirectly (with a demonstrative pronoun), as below:
Among these, this is the best.
Personally, I feel that
～の中で might possibly be chosen over
～で in a formal written style, since the 'full forms' tend to be preferred. But that is debatable and I couldn't offer any evidence to support that. In any case, you can be confident that you can use either variation of it without worrying about making a mistake.