From what I have heard it is one or the other but the net wrap was a problem. Here is something I found in the hay talk forum that seemed interesting but there were others I saw that said the M series net wrap was a major improvement.
I had a 554XL with netwrap and it was a good baler. It liked it's windrows formed consistently but other than that I didn't have any significant trouble with it. The netwrap system was ok but could be a bit touchy getting it to wrap when you changed out rolls. Overall it was a good baler for what I needed. I did end up upgrading to a 604M what was worlds beyond the 554XL as far as capacity and capability. At the time we were moving into more custom baling both on established fields and a lot of slough grass so I needed soething that had a huge appetite. The 554 worked but not nearly as troublefree as the 604M.