MDSV-II are newer condos than phase I. Some people prefer the newer units and others the older ones. Both exchange very well. The older ones are larger and have a fireplace in the living room plus they have better views (imho) but the newer ones are more up to date with cathedral ceilings and a more open plan. I believe the newer ones may not have whirlpools in both bathrooms.
One big difference is that the use of the Spa is free with the MDSV-I but I read somewhere that they were renegotiating a contract with the Marriott Hotel as the old one was running out and I don't know what the outcome is. There is a shuttle bus to the hotel from both properties about every 30 minutes.
We really like the resort and the desert area. There is a lot to do and see.