Technically, the VIP would be better. If you have MC1 and MC2, and you are pointing to the VIP, if one MC is down, the AP would be directed to the other. Reality is that the LMS-IP really is only of significance when a new AP is added to the network. Once the AP communicates with the LMS-IP, the AP is assigned an AP anchor controller (AAC), which the AP stores as the first entry in the node list, which is stored as an environment variable in the APs flash. In addition to the AAC, the other cluster nodes are (randomly, as far as you know, but there is probably some behind the scenes rhyme or reason; I don't know what it is) added to the node list. Any time the AP boots in the future, the AP uses the node list to communicate with the cluster.
So, if you have a VIP between the cluster nodes, point the LMS-IP to it. If you don't, you can either create one, or just point the the LMS-IP to one MC and point the backup LMS-IP to the other MC and you should be fine.
I hope this helps,