I've used both and in my experience, the MAG is much more reliable. It also is now made in a 'light' version which has titainum parts to lighten it. They shorten the life of the weapon but are loved by the men humping up and down mountains in the 'stan. I have gone to the factory where both versions are made several times (it's in Columbia, SC) as part of a military advisory team and the manufacturing is top notch.
The ones I've seen have problems in the field are either broken or have the gas set on the wrong setting. If these guns are properly maintained, they are simply awesome.
The M60 is a great weapon and I'd feel very comfortable going to war with it (as some National Guard units still do) but I'll take the MAG any day.