MR. Hop Up Rubber 60° for AEG

The Maple Leaf MR. Hop Up Rubber 60° for AEG has a wider and larger contact surface making the hop even better to adjust.

The number of degrees says something about the hardness of the rubber. 60 Degrees is a soft variant and 80 degrees the hardest variant. The different hardnesses can be applied in different ways in your AEG.
It makes no sense to use the hardest bucking when it's around freezing point because the cold makes a bucking stiffer and therefore harder to adjust. Especially in cold temperatures, you want a softer bucking.

Also, the hardness of the bucking is also linked to the weight of the bb you are playing with. You can easily use a 0.30gr bb on a 50 degree bucking, but this will probably result in it needing to be replaced faster than when using this weight on, say, a 70 degree bucking.

Ultimately, then, it comes down to personal preference.