Long codes can be used globally, but don’t support delivery receipts, so a business won’t know for sure if the message has been received by the intended recipients unless they respond. However, with SMS-Magic, delivery status can be seen for long code as well. Overall, long codes are not considered to be very stable from a technical or legal standpoint.
On the other hand, short codes are country specific and provide delivery receipts, which are useful in cases like two factor authentication, and when SMS delivery is critical. They are considered to be reliable in both aspects- technical & legal.