A couple of points on this subject:
The article I've attached earlier in this thread (How to maximise yield) provides some thinking material on this subject.
With the guaranteed rental scheme the returns may not be greatest, but you don't have to put any work in yourselves. The downsides are that you often don't get a free hand as to when you (and your friends and family) can use the property, and there are rarely any guarantees on the condition of the property at the end of the two years.
With many rental management companies, you are taking the risk on their performance. This often means you'll make some money if the resort and your property is popular.
If you do it yourself, then it can be hard work, especially in the first months. There are local companies who will provide key holding, cleaning services, etc. Again you are taking the risk, but you get the rewards that go with this. Working together with some other owners, can help with choice of service providers easier, and support group bookings.
Regards David